By the nature of the LLM architecture I think if you "colored" the input via tokens the model would about 85% "unlearn" the coloring anyhow. Which is to say, it's going to figure out that "test" in the two different colors is the same thing. It kind of has to, after all, you don't want to be talking about a "test" in your prompt and it be completely unable to connect that to the concept of "test" in its own replies. The coloring would end up as just another language in an already multi-language model. It might slightly help but I doubt it would be a solution to the problem. And possibly at an unacceptable loss of capability as it would burn some of its capacity on that "unlearning".