What causes change of colour in a cat's fur?

Black color can be "bleached" out to look brown from too much direct sun (sitting outside a lot in the direct sun). To prevent this, you need to keep the cat more inside or provide more shade in an enclosure in the yard.

When the cat sheds out the old coat, the new coat will be blacker again as long as you keep the cat out of the sun.

Also too much licking/washing by the cat can cause a rusty look to black color (or yellow on white cats).

Sounds like a cat that's been free roaming and has "rusting" of the fur from the sun. Can you post a pic?

Emily, you've said this before and once, you're WRONG. Black is black in cats. Perhaps you're confusing cats with horses? Solid Brown and especially Brown and White are VERY uncommon colours in cats.

Most black cats are not truly black - they are an extremely dark brown. If my 'black' and white cat sits in the shade, his fur looks jet black, but when the sun is on him, the black actually looks like a rustyish reddish brown colour, and you can actually see some very vague tabby markings in it since most black and white cats are a massive mash up of breeds.

Fur can also become bleached by the sun, just like human hair - The bits of my hair that don't see the sun are a brownish colour, the bits that do are quite blonde.

Kidney ailment could have many reasons - a scourge, a congenital predisposition, weight loss software, trauma. happening 9 is a minimal of center elderly for a cat, regrettably this ailment isn't that uncommon. Your vet is the terrific individual to tell you approximately plausible reasons for this, and of path medical care thoughts. Kidney ailment isn't contagious, your different cat won't 'catch' it from him. additionally the fleas won't have something to do with it. Have a good long communicate with your vet, they're the terrific to respond to your questions and propose you. Chalice