As of my informations gathering any merch. Food will not change the color of the fh, but in the kok yeah, because the kok is just a fat, if feed a good quality food so your fh is going healhty then there's a possibility that their kok will grow more. If their color is red it will be red forever, if dark then dark forever, but for now dont worry too much because he/she is very young to judge its color, the color of it will change while its growing.