Our Vet gave us good information on the staining you're seeing. Our (actually Mrs. C's) Zuchon is a white coated dog and at the age of about 2 began showing the slightly reddish stains from the eyes, mouth and private parts. The best evidence blames Red Yeast as the culprit. As already stated, the yeast infection can also be invaded by other bacteria... mostly seen in white dogs such as our Bichon Frise cross, but still causing staining in other color dogs... it's just not as visible.
We use a product called Angel Eyes (we're in the U.S.) but the groomer also has good luck with her own concoction of Milk of Magnesia, corn starch (or corn flour) mixed with common hydgrogen peroxide into a paste. We take care around the eyes, of course, but use the paste liberally on the stained areas, let dry and rinse well the next day. She (the groomer) also uses a human hair conditioner following since it can dry the hair. (I refuse to treat the "private parts" though).