With pheasants that isn't the case. With these birds there is some unknown influence happening, I don't know if it's environmental, or nutritional. I haven't changed my feed nor their environment/habitat. All my Yellows from last year's hatch have the Tangerine look to them, so I don't think it's genetics, due to the fact I have 3 different bloodlines, plus the original bloodline I have had for 15 years now. Only until last year has this been evident across all bloodlines.It would appear that it works with a mix of light and dark factor genes then - and darkening with age.
Red Zebra finches have the darkening with age effect too, particularly with the males.