
This is the problem with white dogs, sometimes it's the colouring in food, like beet. I have my dogs on a raw diet, there's loads of info on the web, Google Barf Diet. Raw feeding is much better for your dog and natural too. Also rain water to drink can help as minerals in tap water can contribute to it too.
If your pup is teething it's eyes will be worse and may improve when it has finished. I would leave his eyes alone as much as you can, i wouldn't use any of the bleach cleaners or antibiotic ones like Angel Eyes either. Just wipe them daily with some cool boiled water. Also cut the hair from around his eyes too.
Some are much worse than others and some have no tear stains at all. There are sites like Bichon Banter.
that have suggestions, as its a problem for lot's of small white dogs.
Good luck Helen, they are super little dogs.
Liz R