I have had my cat treated for ear mites and checked time and time again because I still see the brownish
You can see brown little bugs in there ears
If the inside of their ears are coated with black or brownish discharge the probably have them. Check with your vet.
Does it look like mud in its ear?is kitty tilting or shaking its head a lot,then it's probably mites,easy to take care of need to go to vet.
The above answers are all correct but they can also have a smell to the ear , I would have your vet check and clean his ears because this can cause your cat to lose there hearing if left untreated.