Sometimes people mistake ear wax for discharge. Many cats produce larger than normal amounts of wax, so be aware that sometimes that is the reason you see stuff coming out of there. However, you can't just be blasé about it. Ear discharge is often a sign of ear infection or
a case of ear mites. Wax will generally be light brown - that is OK and probably not something to worry about.
Cleaning your cat's ears regularly will reduce this problem. If the stuff coming out of the cat's ear is red, black, or pus (yellow and green and not the same consistency as ear wax - more liquid-like) then it is not OK and you need to see a vet.
What you should watch for is abnormal scratching of the ears. The gunk usually isn't a direct symptom of the disease - the cat scratches, and that repeated scratching causes trauma to the sensitive tissues of the ear and that leads to discharge. This can actually lead to more serious injuries and infections inside the ear canal. Also look for the cat shaking its head frequently, or redness around the ear. You should smell the cat's ears, as well - if there is a bad odor it is a sign of more serious problems.
