I understand what you say. Even I do like to do this. Problem is I am unable to understand the reply of previous post therefore I ask the question in a new post in a different way. If you can delete my previous post.
Well, c.pfaffenbichler said the same thing: Multiply blend mode, which is the correct answer for CMY > RGB. But you need to have a white background, not black.
Going the other way, RGB > CMY, you use the inverse of Multiply, which is Screen, and you need a black background.