Why separate by electrical charge?
First, all quarks have color charge which is always present and is always attractive. The color force holds the nucleus together without preference to orientation. Because the color force is always the same and is always shifting from quark to quark but the color force does not control position or arrangement, labeling of color gluons will be obviated to simplify the presentation of this model Second, The electric charges of the quarks are what differentiates the locations of the protons and neutrons in the nucleus. The up quarks have a + 2/3 charge and the down quarks have a – 1/3 charge. The only position where up quarks are nearest neighbors are in protons and the only place down quarks are nearest neighbors are in neutrons. Everywhere else in the nucleus nearest neighbors of an up quark are always a down quark. The important results is that protons are never nearest neighbors and neutrons are never nearest neighbors, protons and neutrons are always nearest neighbors. This is illust
