> it’s is not my responsibility to validate all permutations of unknown types to ensure you’re passing me mine.
Of course it is! If you provide an API that takes a Color, and you define valid Colors as exclusively Red, Green, and Blue, then you are absolutely responsible for validating input Color values and rejecting anything which is not Red, Green, or Blue. If you delegate that responsibility to the caller, then your API provides no meaningful encapsulation, and isn't a useful abstraction -- it's entirely leaky. No bueno.
Of course it is! If you provide an API that takes a Color, and you define valid Colors as exclusively Red, Green, and Blue, then you are absolutely responsible for validating input Color values and rejecting anything which is not Red, Green, or Blue. If you delegate that responsibility to the caller, then your API provides no meaningful encapsulation, and isn't a useful abstraction -- it's entirely leaky. No bueno.