In this link there is a better exposition of what a proton is, within QCD. The model you are thinking about is really rudimentary and cannot explain the dynamics of Quantum ChromoDynamics, QCD. But as long as you don't worry about which quark is which color, for purposes of this answer it's safe to ignore this. For example, a blue quark could absorb a green-antiblue gluon and become a green quark.ġI'm glossing over some quantum-mechanical details here specifically, a color singlet wavefunction needs to be an antisymmetrized linear combination, like $\frac(rgb - rbg + gbr - grb + brg - bgr)$, not just $rgb$. Given that, it should seem reasonable that gluons change the color of quarks whenever they are emitted or absorbed, in a way that keeps the total color charge the same. Only the total color charge in the baryon matters. The point is that you don't actually have to have a quark of each color in the baryon at all times. Or so on the possibilities are literally infinite. Or two red quarks, two green quarks, an antiblue antiquark, a blue-antired gluon, and a blue-antigreen gluon. You could have three red quarks, a green-antired gluon, and a blue-antired gluon. 1 (Or the anticolor equivalents.) But with all the complicated excitations that make up a baryon, there are all sorts of ways to make a color singlet. Now, if you literally only had three quarks, the only way to make them a color singlet is to have one be red, one be green, and one be blue. There's a simple intuitive justification for this: just as an electrically charged particle will tend to attract oppositely charged particles to form neutral composites (like protons and electrons attracting each other to form atoms), something which has the charge associated with the strong interaction (color charge) will attract other color-charged particles to form neutral composites (color singlets). One of the conditions required of all these excitations in fields is that they be a color singlet, which is the strong interaction's version of being uncharged. These excitations propagate through spacetime and convert among each other as they go, and in a baryon, the propagation and mutual conversion happen to sustain each other so that the baryon can exist as a coherent particle for a while. Quark fields, gluon fields, photon fields, and everything. So you should stop thinking of baryons as groups of three quarks and start thinking of them as excitations in quantum fields - and in particular, excitations in all the quantum fields at once. It works for some purposes, but in this case it causes way more confusion than it's worth. The idea that baryons contain three quarks is a significant oversimplification wrong.