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). 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.
[NAME:rose gold][ADJ:rose gold][COLOR:5:5:1]
[SOLID_DENSITY:19320] used gold
bismuth itself is brittle, but you can alloy it with tin/copper to make a light-colored bronze