If you'll look at the code, parse_bbc_inline DOES process colors, but only if you tell it to use the full set of inline tags.
I think the reason was mostly that I dislike this tag personally, so I couldn't see myself moving it to the shortlist :lol:
And although it can't break designs, it can break good sense. So I'd tend to say, "if you want color tags, make sure to ask for the full set when dealing with parse_bbc_inline."