I know tongue color has a lot to do with general health and I feel a white tongue strongly relates to candida. However, I would need to do more research to say for certain.
As far as the flatulence, he should consider taking juniper berry extract with can reduce flatulence and it also protects your liver/kidneys. If he has a lot of gas, I recommend trying out zypan.
Here’s a good article about tongue health and a person’s health:
I believe in alternative eastern medicine and feel that its very effective from my own experience.
Looks like his kidneys are ailing some based on this article…