Confined

The fact that gluons themselves have color charge causes color charges to be confined while electric charges are not. Confined means that they cannot be found individually, but only in color-neutral composites (hadrons).

When a quark emits or absorbs a gluon, its color can be changed. Quarks emit and absorb gluons very frequently within a hadron, therefore there is no way to observe the color of an individual quark. Within a hadron, though, the color of the two quarks exchanging a gluon will change in a way that keeps the bound system in a "color-neutral" state, so it will stay observable.