I have no intention on getting the full ColorPicker back and running.
Copying colors to wagons was the only thing I ever used it for in the first place.

Usage:

Copy Locomotive and Stop colors to cargo wagons and fluid wagons as you copy other settings between entities.

For Modders:

Mooncat's color mask is added only to base fluid-wagon.
Add this mod as dependency if you wish to have working colors on your fluid wagons.

deprecated for 0.18:

Please support yeahtoasts much improved fluid wagon color masks:
https://mods.factorio.com/mod/FluidWagonColorMask