dog has tinge of pink either side of his white muzzle and also under chin What can i do it,s actually his fur ,because if i part the fur and get to nearly his skin it,s white

It can sometimes be his saliva that is causing the pinking.

so is this food related and what can i do about it?

I have heard that some foods can cause this. What do you feed?

mostly tripe and terrier biscuits sometimes chappie

Saliva, food colourings, chew toys/treats, the soil in your area and even tap water can cause the problem.