There's still no good answer for this problem, it's been around for years, in maltese and white and silver toy poodles mostly. Its a chemical reaction to the fluids from the eye onto the white coat. I believe it tends to be inherited, you might want to talk to the vet to see if the tearducts are blocked, but its likely just something you will have to live with.
Keeping the area as clean as possible will help somewhat but probably not a huge amount.. Sorry.
