Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. I think the darker skin and yellow tinge are not related to vegetable and full grains. I think he is suffering from hiperbilirubinemia which gives yellow color to skin. The causes of hiperbilirubinemia are: *Hepatitis A,B,C D,,E, cirrhosis *Gallbladder stones and colangitis *Cancer of liver or gallbladder *Pancreatitis or cancer of pancreas head *Some medications and autoimmune disease. I recommend him to do: *AST, ALT,bilirubin direct and indirect. *total blood count. Hope I have answered your query. Let me know if I can assist you further.