The bit on the right does look a bit pink. Maybe he has made something sore/bleed if he has been scratching and I think it would be darker then. Is there anything under the Fitch that could make it go pink if wee'd on? (eg coloured food). I guess you're suspecting his pee could be pink. I'm not sure what to suggest - either observe it and see if it happens again or maybe try some diastix that detect blood in urine. A chemist might sell them - something like these - detects blood, glucose, protein etc. I think those are for humans though - not sure if there are special pet ones. Could you phone a vet and ask?
https://www.amazon.co.uk/Parameter-P...o+detect+blood