EB said:
Personally, I think it should, so that variations from the standard color with a cosplay outfit can be searched. I've been doing that with dangerous_beast alternate_color. Though I have been a little uncertain as those cases are often an "alternate" color only in the sense of the character being cosplayed. The change in color is often the standard color scheme of the cosplaying character (not an "alternate" in that regard). Though I'm not sure if a new kind of tag in those cases like "adapted color" would be necessary (adapted costume should apply to that 2B image because of the pattern at the end of her dress, though it wouldn't in the case of a more "straight" cosplay).
I guess that this cosplay is special in its own way, but it probably only add clutter to the tag searches and confusion if we's use an adapted_color tag. I fear that this wouldn't work at all and the two tags will be used inconsequently.
But speaking for other cosplays it would make sense, because I agree with EB here: There has to some way to search for cosplays that are depicted in an alternate color scheme.