What could discolour a cat's coat?

[BertrandRussell]

We have a semi feral/semi stray not sure what he is cat who sometimes spends time with us. We have no idea where he comes from-he just turns up sometimes then goes away again. In the summer he turned up with his fur sticky all round his back end. It didn't smell but it wouldn't wipe off-then he vanished again. Next time he visited, his fur looked very strange, but he was healthy and full of beans as usual. Now he appears to have changed colour-he is still tabby from midsection to head, but gingery from midsection to tailtip. He still seems very much himself-he just looks very odd indeed. Any idea what might have caused it? I assume he got something on his fur-but what could have been that powerful without also making him ill?

Sun can bleach. I have a healthy black cat that goes ginger. There's a vitamin deficiency they can get, too, but it's rare & usually comes with a heap of other obvious, unpleasant symptoms.

Yes, I had a black cat who went gingery in old age because he spent his entire life either asleep in the sun or asleep hugging the Aga. But this is a real half an half effect-I'll take a picture next time he appears!

Has he been rolling in brick dust?

My rabbit appears to spend a lot of time with its head in the shade and back end in the sun and has the same effect.

Could someone have caught him and shaved his back end to treat him?

Regrown shaved fur can come through a different colour. I've seen it in dogs, cats and horses.

Yes, dd's old grey pony has different coloured lines on her flanks- the vet says it's where she was beaten in the past .
If he was shaved,I would like to meet the person who did it- he is quite.......feisty.....to put it mildly.

Did he get oil on his bum, sitting under a car . Would anyone been able to wash him or taken him to the vet to have it shaved off.