Explain why RGB and CMY differ in practice?

RGB and CMY color models differ because they’re based on opposite color mixing principles.

• RGB (Red, Green, Blue) is an additive color model used for light-emitting devices like screens. When all three colors mix at full intensity, they create white light. Mixing red and green gives yellow, green and blue gives cyan, and red and blue gives magenta.
• CMY (Cyan, Magenta, Yellow) is a subtractive color model used for pigments and printing. Pigments absorb (subtract) certain wavelengths and reflect others. Combining all three ideally produces black, but in practice, it creates a dark brownish color — so printers add black (K), forming the CMYK model.

The difference arises from how colors are produced. RGB mixes light directly, while CMY mixes inks that filter light. As a result, colors can look different between your screen and printed paper because of differences in brightness, surface texture, and the medium’s reflectivity.
In short, RGB adds light to create color; CMY removes light to reveal color - one glows, the other reflects.