Rose gold is an alloy of gold and copper, made at a smelter. It is made by combining three gold bars with one copper bar, which results in four rose gold bars. The value of this is a little subjective, as the total material worth of the produced metal is the same as that of the ingredients (3*30 and 1*2 -> 4*23). However, on screen it is a lovely purple color.
Disregarding fuel, you lose the possible utility of the copper bar to get purple-coloured furniture and crafts (for buildings and constructions, bismuth will produce the same color). If you have no magma access then the transition will cost you fuel as well, so it's really a question of how important it is that you get purple metal.
One quirk of rose gold is that is the same density as gold, despite using a much lighter copper bar in its creation. If you're in need of a lot of especially heavy items for your stupid dwarf trick, this bears consideration.
(actually dark blue, but this is less confusing)
temperature values unknown, used gold
value is weighted average of 3 gold and 1 copper
[STATE_NAME_ADJ:LIQUID:molten rose gold]
[STATE_NAME_ADJ:GAS:boiling rose gold]
[SOLID_DENSITY:19320] used gold
[COMPRESSIVE_STRAIN_AT_YIELD:97] bulk modulus 180 GPa
[TENSILE_STRAIN_AT_YIELD:64] young's modulus 78 GPa
[SHEAR_STRAIN_AT_YIELD:185] shear modulus 27 GPa