Python "look-behind requires fixed-width pattern" – Regular Expression Error

I have this regex, it matches a certain word if a list of word are not found:

(?<![Yy]ellow |[Bb]lue |[Rr]ed |[Pp]urple |[Bb]lack )[Cc]olor

It works, but I get the Regex Expression Error: "look-behind requires fixed-width pattern".
I do not have access to the python code.
I tried delimiting by (?:^ and |$) as I saw in a similar question but it didn’t work.
I also found this answer that I think solves the problem but I don’t understand how to make it work in my case.

Test HERE

Dark Color          #match
light color         #match
Blue Color
red color
that is a blue color and theme
opaque color        #match
purple color

>Solution :

You can split up the alternatives in the lookbehind with separated loopbehind assertions if you want a match only:

(?<![Yy]ellow )(?<![Bb]lue )(?<![Rr]ed )(?<![Pp]urple )(?<![Bb]lack )[Cc]olor

See a regex demo

If you have no control over the Python code, you might check if matching what you don’t want and returning a capture group for what you do want also works:

(?:[Yy]ellow |[Bb]lue |[Rr]ed |[Pp]urple |[Bb]lack )[Cc]olor|([Cc]olor)

Regex demo