Color | undefined; tells me that the dev who wrote the code doesn't know whether they will pass the parameter or not, it gets decided at runtime. Not only does

Color | undefined; tells me that the dev who wrote the code doesn't know whether they will pass the parameter or not, it gets decided at runtime. Not only does this complicate the function signature, it inevitably adds a conditional inside that method -- or passes the buck down the line to another method called from within. At that point, TS is just a burden.