Hey Frank,
Co-dominance is pretty cut and dry like recessive genes and not something that is normally found in nature. In fact, co-dominance seems to occur less than recessives do. At least that's how it is in captive collections thus far.

Here are a few definitons of co-dominance.

A condition in which the alleles of a gene pair in a heterozygote are fully expressed thereby resulting in offspring with a phenotype that is neither dominant nor recessive.

(genetics) (of genes) having both alleles expressed equally in the phenotype of the organism

As you can see from the definitions, it is not just a random mixing of phenotypes that brings about co-dominance. It is a rather specific genetic event.