He loves a dust bath as much as any of my hens, but there is a big difference between his colouring and the colouring on my Light Sussex hens who have stayed pristine white. There was something else going on.
Brassiness is the term used to describe the colouration of white turning yellow. Think of any one who has tried bleaching their own hair only to have to turn out not quite so white. That's what can happen to certain feathers, too. Its the colour gene that is affected in some breeds of birds, making some more susceptible than others. The sunlight activates this gene. White ducks may also experience this too. It is not just isolated to chickens.
As the poultry spend a lot of time free ranging in my yard their backs are the most affected as that is where the sunlight is the most concentrated upon them. So a yellowing back but lighter under-carriage is usually the pattern seen from solarisation.
Providing more shaded areas or a shaded run may assist in reducing the brassiness.
Normally, when we feed poultry a diet high in corn we see more yellowing pigmentation of the legs and skin beneath the feathers. In some breeds it can translate to feather discolouration. Other parts of the diet could also be to blame such as being fed a too much leafy greens, marigolds or other rich grasses.
Cutting back on these treats and finding other options may help to decrease this colouring.
Some breeds are more likely to discolour than others, and sometimes its really an individual's make-up.
There are two basic genes in birds that determine colour:
For black and brown colourings
For yellow and red colourings
This brings me back to how much my rooster loves to dust bathe, but usually dust bathing is not the problem at all as it is fine and loose, having been sufficiently worked up by the bird before bathing.
Stains on the feathers are more likely to be from running through areas that rub up against the bird such as under certain bushes, through a various terrain and being exposed to muddy areas.
These stains are most likely to occur during winter or wet conditions. To some degree are able to washed off in preparation for showing.
Using a bluing rinse solution in the washing water will help to clean up the feathers. Alternatively, use a splash of white or apple cider vinegar in the washing water.
The change of feather colour is in no way harmful to the bird, so if you can live with it, then don't change a thing. But if showing off your pride and joy is important to you, I hope these tips can be of some help to getting those lustrous whites shining again.