Cat changing colour

[EATmum]

Our boy is nearly four years old, and is a black and white moggy. Or he was anyway - in the last few months his black has started to go brown. His sister (who we lost very sadly a few weeks ago in a car accident) was a tabby, mainly white.
Is this common/known? I've never known a cat to actually change colour before ...?
TIA

I've known a black cat whose fur turned a reddish brown in the sun.

Yep it's the sun.

There may be other causes, but it's known that black cats can go brown if their diets are deficient in certain amino acids that are involved in melanin production. Here's some info.

our cat has a black winter coat but his summer coat is brown.. ( however I think theres some Burmese in there somewhare , he has an 'oriental look about him)

I hate to break it to you ladies, but it's December.

Loss of black pigment is often caused by deficiency of the amino acid tyrosine, or by copper deficiency/ excess zinc, which indirectly affect tyrosine levels. what are you feeding the cat?
I've also seen it with fairly severe skin disease e.g. Flea allergy dermatitis, and in very elderly (late teens) cats. It can be linked with liver and kidney disease but it's unlikely to be the only sign of those.
A trip to the vet to rule out other problems called for. If all is ok changing diet or a tyrosine supplement should help.

She might be in Australia!

OK, thanks everyone. In all honesty, he doesn't seem like a brilliantly well cat. We've taken him to the vets a couple times because he lost a lot of weight - they've said that he's just settled to his adult proportions. He eats a lot - I think anyway. About five sachets of food a day. Does that seem like a lot to others? Our old cat barely went through one sachet a day, but she had a lot of dried food which he doesn't seem to want. He used to throw up a lot but (sadly) since his sister died he doesn't bolt his food so much. Because of his sickness, we've tried every kind of cat food - he seems to stomach the Aldi sachets more than most - but Whiskas doesn't work for us at all. I will look into the hormone stuff - makes me sad that there might be something more serious going on, but maybe we can help him get some resolution. Thank you all for your wise words.

Eating but losing weight would merit a trip back to the vet.
We have a skinny cat who has gone from black/white to brown/grotty cream colour but she's 18!

Thank you to everyone who commented. Sadly it looks like our boy has FIP, which is very hard to bear. The vet seems to think that he was fighting the coronavirus when his sister got knocked down and killed a few weeks ago - and that grief/stress has lead to the current condition. Very hard, with him here on my lap, to think that he is so poorly at such a young age.

Oh no, that's awful for him. What's the prognosis?.

Sadly it's poor Fluffy - thanks for asking. If it is FIP (a mutation of common virus) then it's always fatal. We're hoping (naively) that it hasn't mutated - but given the other indicators, that's probably a false hope.

So very sorry to hear that. As you say, just have to hope for the best, and prepare fir the worst and make the best of what time he has. [kibble]