With regard to your concern I would like to tell that the normal color of the human tongue is pink to red. In some people the tongue tends to be more red than in others but this is not necessarily a discoloration of the tongue. Glossitis is inflammation of the tongue that may arise for any number of reasons. The process of inflammation increases blood flow to the tongue and leads to redness, pain and swelling. The more common causes of glossitis are acute mechanical or chemical injury or infections. Vitamin deficiencies as is seen with vitamin B12, niacin or folic acid may cause a strawberry red tongue. Scarlet fever (scarlatina) is a condition that may sometimes develop in a person with streptococcal pharyngitis (strep throat). It presents with a red rash that covers most of the body along with a strawberry red tongue. Scarlet fever arises as a reaction to the toxin from the streptococci (bacteria) that causes the infection. For these cough have you not given any medicine or showed any doctor ? If you are giving medicine the colour may be due to that also.I would check his blood for CBC and related tests,if you have not done so far. I have outlined the diseases I would think of limited resources I have got. Please review with your doctor and get back please. Regards