My friend has suggested that the dark brown reddish stain under my pups one eye could be due to red yeast a bacteriaL INFECTION
If so how can i check this is so and how do i treat it?

I would suggest the best thing to do is get a vet to look at it. It's probably tear staining, but you'd need to find out why one eye was running more than the other. The vet will be able to find out why and recommend the best and safest treatment - eyes are too precious to experiment with.

Its so strange as there in no wet under the eye at all and no blinking or sign of him rubbing but he is slightly mismarked as there is white close to the eye where it should be brown If it were brown you wouldnt know it was stained

Red yeast can be in the tears and cause the staining.  The only thing i know to clear it is Angel Eyes unless you can convince the vet to give you AB's.  Can also be transfered if on the paws and rub the eye.