co-dominance means there are always two alleles for any 
character. If the two alleles are equally dominant over one 
another and neither of them exprasses to outside is called 
codominance.Here neither of the character appares in 
offspring.This phenomenon can be clearly explained by 
taking the example of drosophila.

when two allele is dominant

When both alleles of a pair are fully expressed in 
heterozygote,they are called codominant.

both alleles are equally dominant,both alleles are 
expressesd at the same time.
ex. (chicken feathers)
I hope u will like my answer

when two alleles are eually dominant and neither of 
characters appears in offspring. (eg:drosophilla,chicken 
feathers..)