I couldnt find much on the internet.
The New Animal Doctor's Answer Book By Michael W. Fox
Another blurb:
Low protein diets may also be a factor in coat colour change, because tyrosine, an amino acid, is important for the production of coat colour, but low protein diets contain less tyrosine than normal diets. The carnivore connection to nutrition in cats (no abstract provided, but the document may be found here (2002) Zoran D Journal of the American Veterinary Medical Association 221 pp1559-67 explains more about this (see page 3). The addition of tyrosine to the diet, may help, but this is not essential, and should not be done without your vet's approval. See also Dull Coat/Dandruff/Spiky Fur.
If your cat has any Siamese genes, the points may darken as a cat ages. The coat colour of Siamese and Himalayans (colourpoint Persians) is actually determined by temperature changes. As cats age, their circulation often worsens, so their extremities become cooler and their points get darker. However, sick cats with Siamese genes who have a raised temperature (e.g. because of an infection) may actually develop lighter colour fur. In either case, it is normally nothing to worry about.
Red hair in black cats is reversed by addition of tyrosine to the diet (2002) Morris JG, Yu S & Rogers QR The American Society for Nutritional Sciences Journal of Nutrition 132 pp1646S-1648S discusses how the absence or presence of tyrosine in the diet affected the coat colour of healthy kittens. What makes a black cat's coat turn reddish brown is an article from Cat World. The University of Alaska has some info on Siamese coat colour changes. source:
http://www.felinecrf.org/symptoms.htm
I'll ask the science community as well.