In the unlikely event that your black cat has turned a rusty red in normal lighting conditions, there is a possible cure: change his food. Food can alter the appearance of a cat, specifically the colour of his coat. You may have heard of this. It is an interesting topic but, if I am being honest, not of great value because I believe that a rusty coloured black cat because of a lack of tyrosine is probably rare.
Many foods such as fish contain a ingredient called tyrosine. It is an “amino acid” but I won’t dwell on the technical stuff. I am sure it is added to commercially prepared cat food.
Tyrosine (more accurately called “l-tyrosine”) is needed for the creation of the colour in a cat’s fur. The blobs of colour – pigment – in the hair strands are made (“synthethised”) from tyrosine. There are two types of pigment in the hair strands of a cat: eumelanin and pheomelanin. Eumelanin is brown/black and pheomelanin is yellow/reddish brown. They are collectively referred to as “melanin”. The amount of melanin in the fur determines coat color.
An inadequate amount of tyrosine in the cat’s diet results in an incomplete amount of melanin deposited inside the hair fibres. It appears that this relates to the eumelanin component leaving the pheomelanin to show its color of reddish brown. Or perhaps the pigment is thinly spread through the hair turning brown/black to yellow/reddish brown.
It is interesting to note that the amount of typrosine required to ensure a full amount of melanin in the fur is greater than the amount needed for a kitten to grow normally (as I understand this tricky subject). That would imply that black hair might normally be rusty colored. In fact this seems to be true because black cats look rusty red when backlit – the light shines through the hair strands (see picture).
So, in conclusion, if your black cat has turned rusty colored just make sure he has a supplement of tyrosine. That is a simplified conclusion and don’t do anything without talking to your vet first, please. There are other potential causes of colour change.
Incidentally, tyrosine supplements for people can be bought over the counter. It is used to treat mental health conditions such as chronic fatigue syndrome and attention deficit disorders.
Interesting fact: the pattern in a cat’s coat is mirrored in the skin. However, polar bears have pigment-free hairs but black skin. Melanism is the effect of a patterned cat (usually brown tabby) turning black with a ghost pattern due to a genetic mutation.
Note: the information for the article comes from the Journal of Nutrition.