I don't know any language where "colo[u]r" is a keyword, or a lexer-level entity tbh, so I'm not sure there would be any difference. Anywhere you can name a variable "color", you can name it "colour". C++ allows you to explicitly make one an alias to the other, for example.

That said, I've seen a number of BBCode parsers need to take both "[color="] and "[colour=]". Really, we need code and programming languages in general to be less American. It's 2023 already and in many programming languages I have to name my accounting variables "ano" (butthole) instead of "año" (year).