I can't make a diagnosis from the pics.
you can get red marks on a fish from septicaemia which would be quite serious - its an acute bacterial infection of the entire system...treatment if so would I presume be maracyn/maracyn 2, a broad spectrum anti-bacterial agent. White spots on a fish are often ich, which is treated with raised temperature and salt.
Please don't however go treating him with this until you have a good diagnosis.
In the meantime can you tell us what is your tank size, other inhabitants (or is it just the two comets?) and test results for ammonia, nitrite, nitrate ? It would also help to say what test kit you used.
The reason for this is that fish disease is often brought on by poor water conditions, and equally if not more important than any medication is keeping the water pristine if they are to recover.
edit : is the tank your 20 gallon ? it may be getting a leeeeetle bit tight for the 2 comets, which will not help any in maintaining good water conditions (0 ammonia, 0 nitriate, some nitrates)