RGB colour and paint colour are different things.
RGB can exhaustively list all the colours available via additive mixing of the narrow bandwidths of light emitted by red, green, and blue LEDs. Our eyes are reasonably good at filling in the blanks.
But there are far more bandwidths of visible light NOT emitted by red, green, and blue LEDs - so any colour made by full-spectrum white light bouncing off a mixture of pigments, cannot be accurately represented as RGB values, nor accurately reproduced on an LED screen.
A screen showing 255-255-255 does not look remotely the same as sunlight bouncing off a wall covered in titanium dioxide based paint.