Is it ear wax or is it pus? If it's a yellow discharge you might want to check whether it is smelly. If it is you might want to call your pediatrician as it might be an ear infection. Babies are prone to ear infections during recovery from a cold. If the discharge is still around after 3 days, do drop your pediatrician a line. Usually ear infections will clear up by itself but if it doesn't, you'll know because your baby would most likely develop a fever.
For more info you can read this site: Ear infections