Thank you for sharing those nice pictures of Charlie. Changes in hair color in cats is not very common but it does happen from time to time. Although I am not sure I have enough of Charlie’s history to thoroughly answer specifically; here is a summary of what I do know on changing hair color in cats.
Hair color is mostly genetically controlled but several factors can influence the color of hair:
1- The Diet:
Diet deficient in the amino acid thyrosine and/or phenylalanine causes the hair color to change from black to reddish color with a reduction of the pigment melanin in the hair. The requirement is 18 mg thyrosine + phenylalanine/kg diet.
Copper deficiency or zinc excess may also cause achromotrichia; a complicated word that means loss in hair color. Liver, kidney or thyroid deficiency can also cause the same change in color.
2- The Environment:
Lightening of the coat can occur with excessive exposure to chlorinated water (cat spending too much time around the pool) sunlight or if the hair growth is very slow.
3- The Skin Temperature:
Skin at a higher temperature has lighter colored hair and cooler areas have darker hair. So for example if an area is clipped, it is cooler and therefore hair re-growth is darker. Different outside temperatures and hair density could have similar effects.
In the case of Charlie, one thing to determine is what was his normal color: The lighter colors in the beginning (in this case, the question has been solved by his change of diet) or is his coat the darker color now? Please also keep in mind that several causes may exist at the same time.
Omega-3, although certainly helpful with maladies, it will not do much for the color of the hair. Charlie has other good reasons to be supplemented with Omega-3 but not this one! (You can read more info on ArcaNatura’s blogs.)
Let me know if I have answered your question.
Serge Martinod, DVM, PhD