[virchau13]

Could it be possible to infer optional colors from the environment?

You denote that the color is optional in the function's type signature, and inside the body of the function, you have a construct that lets you execute different code depending on the state of the function's colors. The call site could either automatically infer the colors used or the colors used could be manually specified.

Basically a type parameter with compile-time if statements.

[xigoi]

So, algebraic effects?