You could try some of these natural approaches.
"There are no proven cures for the pigment problems mentioned here, but anecdotal recommendations abound. For example, supplementing with melatonin, the hormone associated with sleep, may help with seasonal changes. Vitiligo may respond to oral doses of folic acid (1 mg twice per day for an 80-pound dog) combined with vitamin C (500 mg twice daily) and injectable vitamin B12 (50 micrograms every 14 days). Some dog owners have reported success giving blueberry extract.
Juliette de Bairacli Levy’s natural rearing methods have been popular since the publication of her Complete Herbal Handbook for the Dog and Cat in 1955. “I introduced seaweed to the veterinary world when a student in the early ’30s,” she said. “It was scorned then, but now it is very popular worldwide.” She credited kelp and other sea vegetables with giving dark pigment to eyes, noses,
and nails, stimulating hair growth, and developing strong bones.
It’s important not to overuse kelp; it’s rich in iodine, and too much iodine can suppress thyroid function. Levy’s NR Seaweed Mineral Food contains deep-sea kelp, nettle, and cleavers or uvi ursi, herbs that are associated with thyroid, skin, coat, and kidney health. The recommended daily dose is a pinch for small dogs, 1/8 to 1/4 teaspoon for medium-size dogs, and 1/2 teaspoon for large dogs. Kelp fed by itself should be limited to half these amounts." CJ Puotinen and Mary Straus
I have personally used the above NR product along with other Juliette de Bairacli Levy's "NR" products, (although not for snow nose), everyday, until our dogs were 2 years old and was very pleased with them. I now rotate them in occasionally.
You can purchase the full line of "NR" products at NaturalRearing.com :: Loading Website...