Here you can find a list of all ingame shown colors and all stones, ores, metals, alloys, gems, glass , trees, "liquids" and ice with that color.
 Niggys Color helper!
All thanks to Quietusts for removing the redlinks!
Stones Chalk, Limestone, Dolomite, Rock salt, Marble, Quartzite, Alabaster, Alunite,
Stones Borax, Calcite, Cryolite, Marcasite, Periclase, Satinspar, Selenite, Talc
Ores Native aluminium, Galena, Horn silver, Native platinum, Native silver
Metals Aluminium, Platinum, Silver
Alloys Fine pewter, Nickel silver, Sterling silver
Glass Crystal glass
Gems Fortification agate, Jasper opal, Milk opal, Milk quartz, Moonstone, Onyx opal, Pineapple opal
Gems Pipe opal, Rock crystal, White chalcedony, White jade, Bandfire opal, Cat's eye, Clear zircon
Gems Crystal opal, Goshenite, Harlequin opal, Light yellow diamond, Pinfire opal, White opal, Clear diamond
Trees Feather tree, Tower-cap
White is not very hard to find in certain biomes since 6 white blocks form entire layers, with marble which is nearly everywhere, but without those, white has only more stones that are not very common, so it can be easy or hard to make a white fortress. White also posses the second most valuable metals, platinium and aluminium, and also siver. With 2 white trees, white has the second most trees after brown.
Stones Granite, Dacite, Gneiss, Phyllite, Anhydrite, Pyrolusite, Stibnite
Metals Nickel, Tin, Zinc
Alloys Billion, Trifle pewter
Gems Bone opal, Clear tourmaline, Dendritic agate, Gray chalcedony, Onyx, Shell opal, Clear garnet
Light grey has 4 layerforming stones, but after that only three uncommon stones. It also has only 1 ore, 3 metals,2 alloys and no trees with its color, so its harder to make a light grey fortress.
Stones Claystone, Shale, Diorite, Gabbro, Andesite, Basalt, Obsidian, Rhyolite, Slate, Chromite
Stones Graphite, Hornblende, Ilmenite, Jet, Lignite, Mica
Ores Magnetite, Sphalerite, Tetrahedrite
Metals Iron, Lead
Alloys Pig Iron, Steel
Gems Morion, Schorl, Black opal, Black pyrope, Black zircon, Melanite, Black diamond
9 layerforming stones has dark grey and with that even more than white. I would say, dark grey is the easiest to find color currently in DF (Without gems), Since it has the most used metal (iron) and the most used alloys (pig iron, steel) and many common stones.
Stones Chert, Conglomerate, Mudstone, Sandstone, Siltstone, Schist, Puddingstone
Ores Cassiterite, Native Copper
Gems Amber opal, Brown jasper, Fire agate, Picture jasper, Plume agate, Smoky quartz, Tube agate
Gems Wax opal, Wood opal, Brown zircon, Cinnamon grossular, Honey yellow beryl, Jelly opal
Gems Faint yellow diamond
Trees Acacia, Alder, Ash, Birch, Cacao tree, Candlenut, Cedar, Chestnut, Highwood,
Trees Kapok, Larch, Mango tree, Mahogany, Maple, Mangrove, Oak, Palm, Pine, Rubber tree
Trees Saguaro, Willow "Liquid" Mud
With 6 layerforming stones and only 1 non layer stone which only occurs already in a brown stone, it can be dificult in many biomes to find brown stones. But it has many, many trees (all overground trees except featherwood and glumprong).
Stones Bauxite, Kaolinite,
Gems Banded agate, Bloodstone, Carnelian, Sardonyx, Sard, Almandine, Red grossular, Red pyrope
Gems Red spinel, Red tourmaline, Red zircon, Ruby, Red diamond
Trees Blood thorn
The first color without a layerstone but with the most valuable stone in previous versions (bauxite) it is quite hard to make a dark red fortress, but who has one is always pleased to see its fortress "bloodcovered".
Stones Brimstone, Gypsum, Orpiment, Orthoclase, Saltpeter, Sylvite
Ores Native gold, Limonite
Alloys Bismuth Bronze, Brass, Electrum
Gems Citrine, Gold opal, Pyrite, Resin opal, Sunstone, Tiger iron, Tigereye, Yellow jasper
Gems Golden beryl, Levin opal, Rubicelle, Topazolite, Topaz, Yellow grossular, Yellow spessartine
Gems Yellow zircon, Yellow diamond
No layerstone, but many common stones, it is quite often that a fortress has many yellow stones.
Cinnabar the fake ore, petrified wood, the only magmasafe wood and realgar it has one vein stone and two small cluster stone, makes light red a very uncommon color.
Cobaltite the second fake ore is the only building material of light blue.Very uncommon.
One uncommon stone and one uncommon tree, nice color but very rare.
Even with only one stone and the most valuable metal ever (adamantine) it is quite common since microcline is everywhere. And Ice is neat renewable source of light cyan. My favorite color.
Only the ore of nickel has light green, which is another rare color in fortresses.
Stones Olivine, Serpentine
Glass Green glass
Gems Aventurine, Moss agate, Moss opal, Prase opal, Prase, Variscite, Demantoid, Green tourmaline,
Gems Green zircon, Tsavorite, Emerald, Green diamond
Olivine is quite often and green glass is a easy to create glass, so its no so uncommon to have a dark green color.
Pitchblende and rutile are very uncommon stones that only occur as small clusters and a tree that only grows in evil biomes. Very rare.
One alloy, one glass, one tree. Very rare.
One metal, one alloy, one tree. Pretty much the same like above.
If you have more things to add (Maybe leather, what ever else has colors), feel free to add it.
 My idea on "Why do creatures stay at certain sites"
There should be certain reasons if a creature stays(not visits) at a site (like your fortress) and if these are not met, they will go away or insane if they can't do the first.
List of reason to stay or not: 1: This is my home: Basically, the creature wants to live here, this applies to your normal dwarves and immigrants but also goes into account of every other creature. If the creature is happy it will stay, if not it will go (not the normally insane) and leave your fortress.
2: That guy is not letting me go: This would apply to all slaves in your fortress. They will attempt to flee if they don't fear the consequences enough or they will try to revolt if they have weapons.
Things that increase the force (to stay here): -Seeing a family member/friend/creature of the same race/other slaves (in order of the highest to lowest effect) dying while attempting to flee/revolt -Being chained/caged (This will increase the fear greatly) -Getting punished -Seeing family members/friends/creatures of the same race/other slaves getting punished for whatever reason (Lava pit diving is much more fun, if you let goblin slaves do it) -Being far away from every exit (depends on distance) -Walking in a trap while fleeing/revolting
Things that decrease the force(to stay here): -Seeing a family member/friend/creature of the same race/other slaves revolting/fleeing -Having access to some weapons (only revolting, don't let slaves haul your adamantine weapons) -Having an open exit (fleeing only, don't let slaves outside) -Seeing members of the enslavers dying (while an ambush or siege)
Things that affect the force level -Being self confident or not (Affects chance of revolt more than fleeing) -Being brave (Brave creatures prefer revolting and dead than being slaved, fearful creatures prefer living and fleeing) -Getting spirited by a creature with a high leadership (revolting only, may also have drawbacks for creatures that hate each others)
3: I stay here because I am paid to do that: Mercenaries will ocacially visit your fortress and will stay there if they get some money and/or a home to live in. These will go if they don't get paid.
4: Loyality : Certain creatures can form loyality to other creatures, the crown guard to their king, a young mercrenary to an old master of fighting, slaves for getting defended against some things, "fathers and mothers to their children" (could be counted as loyality), an animal to its owner, even creatures can get attached to certain landscapes (I will never leave this cage, its to epic).
Creatures which have loyality to different creatures will not flee if their object of loyality does not flee. In opposite, they will flee if their object of loyality indeed does flee.
5: Wander mood: Kinda liken the current strange moods, a creature may walk away to wander the world instead of staying at home.
All reasons to stay or not, will be put together. A slave may form loyality to his comrades or his family and will not flee even when able to. Or a former mercrenary will settle in your fortress because he want to life there.
 Slaves! (A evil (normal?) fortress master dream)
Basically every creature that has the [CAN_LEARN] and [CAN_SPEAK] or [INTELLIGENT] tag can be enslaved. To enslave a creature (maybe the last goblin ambush) you need it to be caged. Then you assign it to be enslaved and your Slavemaster dwarf (a new job maybe) would go to that cage (like pet taming) and start to do his job (beating it until it gives up, a whip can help). After you have atleast one slave, you must make slave quarters, the future homes of your slaves. Decorate it nicely with some metal doors and cages and chains hanging from the roof. Slaves don't need beds, so don't give them some. You should also keep the slave master in the near of his charge so they can feel his love, a iron whip, it menances with spikes of iron. When you have setup everything, you can assign the slaves to your normal dwarf or assign them work directly. All slaves can do any work, or they could take a part in your armie. "RELEASE THE TIGERMAN!"
Poorly, a slave needs food like everyone else. You should make a small food stockpile in their quarters and also a small, nice well. Watch them, when 20 hungry slaves after hard days to work, all storm to the last piece of bread in their stockpile. As with every animal, slaves will occiacially pop out some children. These can be very helpful, as they are new slaves which will occacially produce new slaves and fun toys. They may even ask you if you could allow them to marry each other, this can be useful, or not. Or its just funny seeing as you deny this. There is also nothing more fun then tossing the new born elf baby slave into that lava pit over there. :D Its good to be evil (or normal).
If you are feeling really happy, you can even give freedom to new grown family, and make them real members of your fortress. Or not. Most likely not. If you are a child snatching race, you can use this to produce even more slaves. Or just trade them. Slaves are very useful in every direction.
Just don't let them haul your collection of adamantine weapons, as this can give slaves bad thoughts and cause some fun in the form of a armed slave revolt.
 Magic (some sort of thing that will be in DF one time)
Magic could have different directions to go into, every creature can go into one certain direction of magic but will only be truly a master if it specialises on one direction:
Healing, Magic alchemy, summoning, demonic magic, necromantic, magic enchanting, mind controlling, elemental control (either in all directions or focusing in one element: fire, ice, water, light, darkness, thunder, earth, wind, life, death whatever else may come up), magical crafting
Healing: Healing wounds, curing poisons, removing rot, regrowing limbs, on highest level maybe even resurrection? Is directed to necromantic, and elemental life control
Magic alchemy: A fusion of alchemy and magic, will produce much better alchemic results with less time and work
Summoning: Summoning or calling of normal creatures, magical spirtites, elemental golems or even deities (priests could perform this to send a call to their deity). Would be related to all sorts of elemental control, necromantic and demonic magic.
Demonic magic: Enslaving the power of called demons to use under your control. This will provide enourmous powers but could end to endless pain if the demons overwhelm you and take you with in their world (like in here) which WILL happend if you are growing older and older. Related to summoning.
Necromantic: Reviving the fallen by channeling your own powers to move their bodies like puppets will not touching the soul of the dead. Unlike reviving through healing or elemental life, this will not provide a own will of the revived but its much easier and you gain more control of the dead. The zombies and skeletons and whatelse can be from any living creature, but can be overtaken by a greater might, like a force, deity or demon. Related to summoning, healing, mindcontrolling, elemental death and life.
Magic enchanting: Altering the properties of certain materials, tools or weapons. This alters the old properties greatly depending of the magican. He could enchant a copper dagger to be as strong as a steel dagger and as hot like dragon fire, while not burning its wearer. Related to all elemental controls and magical crafting. This can be done at any point the to-enchanting obejct exists, unlike magical crafting which will only work on the creation of the object. Enchantings will loose its power over time, the enchanting will stay longer, the better the enchanter is.
Mind controlling: Enslaving or affecting the mind of any creature, and changing its behaviour. Removing all fear, deleting all memories, or full remote control of its body. Related to elemental life and necromantic.
Elemental Control: Directly controling or altering the flow of elementals, sending a fireball there, changing the path of a thunderbolt here and freezing the next test subject. Some elements can be controlled by other elements, like if I remove all heat of a place, ice and coldness will spread there. This is called indirect control. Direct control can move the element, increase or decrease its strenght and other things.
Magical Crafting: Using magical powers to work magical abilities into a material. These will stay forever until the destruction of the object, then they will break out in the form of a small magical explosion. Related to magical enchanting.
All forms of magic must be learned by the individual, before it can use and master them. Some creatures are more affected by magic then others, while even some species are more affected by certain ways of magic then others (elves in healing and elemental life and light, dwarves in enchanting, magical crafting and elemental earth). To train a creature in magic, it needs to pose magical affection and a magican needs to find this affection in order to train it into a magican. It can also gain powers through objects (a magical hammer for crafting for example) or as a present from a deity or demon.
In fortress mode, you could get a immigrant magican, who will then start to live in your fortress and increase its ability in his/her magical direction. Upon finding another magical affected individual, the magican will start to train (if you allow it) the apprentice in general knowledge of magic. The apprentice will choose from a magical direction it likes but will prefer a direction an already existing magican uses.
The apprentice will test its new won abilities on some subjects, like necromantic on dead creatures (the latest siege will help here), like healing in the hospital or manipulating the elements outside (or worse, inside) your fortres.
Imagine to see your newest apprentice to test his necromantic powers in the graveyard of your fortress!0