Right now, there are several inconsistencies with which colors are valid for which tags and I believe there should be a universal list of valid colors that apply to all colored tags (*_hair, *_eyes, etc.).
From what I've see, the following colors are universal1:
- black
- blue
- brown
- green
- grey
- orange
- red
- pink
- purple
- rainbow (not one color but is treated like one)
- tan
- white
The following colors are not1:
- amber (light orange, only applies to eyes)
- beige (sometimes aliased to tan)
- blonde (hair only, aliased to yellow elsewhere)
- cream (sometimes aliased to tan)
- cyan (sometimes aliased to blue)
- teal (sometimes aliased to green)
- yellow (everything except hair)
1 I may have missed a few. I left out really obscure colors like olive (dark yellow) and maroon (dark red).
The big problem with these inconsistencies and the aliases enforcing them is that you can have images where several things are the same color yet you can't tag those same colored things as the same color because some automatically change to something else. It also affects one's ability to find images containing that colored thing.
Examples:
post #190748 <- yellow hair and fur, but can't tag yellow_hair.
post #862133 <- teal hair, fur, eyes and skin, but can't tag teal_fur.
post #1099942 <- tan and beige fur, but can't tag beige_fur.
Updated by Volteer133