In SU(3), the three complex fields in global gauge transformation can be identified to the three quark fields (u, d, s), which can be thought of as the three directions at 120o to each other. It is called colour isospin or colour spin or colour charge (r, g, b) in local gauge transformation.|
The SU(3) group has Na = 8, there are eight phase angles and eight 3x3 non-commuting matrices (generators) operating on three complex functions (u, d, s) or (r, g, b) depending on whether the transformation is global or local. There are eight corresponding meditation particles (the gluons) - two of them mediate the strong interaction while the rest go around to swap color charges. (see Figure 02d).