The yellow is a Male kenyi, who's comfortable enough to show he's male! Doesn’t have to be the dom male in the tank.
However it mean's HE is thinking of himself as the Dominate kenyi male, if you have another male kenyi it wont stay that way long, my kenyi male has 4 female's in a mixed tank and doesn’t bother any of the other species, he will however kill any other male kenyi who turns yellow
And just to ad, tank hierarchy is based on not only the fish, but the tank and territory, a hierarchy will not always establish itself in the same order even if it's the exact same fish, quite the opposite a change in scenery can be all that's needed to give a sub dom male that push to try and form a territory of his own and become top dog! If you do have other yellow kenyi in the same tank I suggest picking the niest and removing the rest, your gonna end up with only one in the end anyway, might as well choose for yourself rather then let them kill eachother!