The intensity of the spawning color in these char is strongly influence by the dominance of the fish. The more dominant the male the more highly colored the fish will be. For this reason the largest males are usually the most highly colored.
It might also be of interest to know that the fish can change how brightly they are colored very quickly. In a situation where there are multiple males the most dominate fish will be the most highly colored. If that dominance changes for some reason the previous dominate male's color will fade quickly while the new dominate male color will intensify. This flip in coloration can occur in less than 5 minutes.