RGB values are pointless when talking model colours, though. They're probably a good starting point if you want to make a 3D model not for printing out but for use on a computer screen, but pretty much no use for mixing paint to.

For starters, RGB is an additive colour model because it's designed for use on screens that beam light at you. That is, rgb(0, 0, 0) is black and rgb(255, 255, 255) is white, because with a pixel all the way off (all colour values 0), there is no light coming from it.

Paint, OTOH, represents a subtractive colour: light from an external source hits the paint and some of it gets absorbed by the pigment. All the light that isn't absorbed bounces off and can hit your eye.

Though this may seem like it's just achieving the same result from opposite sides, it actually makes for different perceived colours.

Add to this the fact that colours on a computer screen are dependent on that screen's settings and particularities, and the outcome is that any colour on a screen is little more than an approximation of the "same" colour in paint or ink.