Because quarks are permanently confined, the circle state is always a virtue state. Because quark intrinsically can be any of the three colors, the uncertainty principle permits it to change to another color. But the color complementary rule forces its confined quark partner changing into a different color when one quark changes the color by quantum uncertainty. Quark colors are conserved in the prequark representation of neutron decay. The prequark representation of proton or neutron is very much similar to glider.
Prequark model gives much more detailed and clear picture.
Proton is not composite of only three quarks but includes gluons, spin, electric charges, weak charge, etc. However, prequarks are not particles in the traditional sense, such as proton or quark. Prequark is not a particle in any sense. Prequarks are attributes of the space-time world sheet. We can view Vacutron as the valley bottom of the space-time world sheet, Angultron the summit of the hill.