Here, maybe this is where the misunderstanding between you, in the reptile buis, and me in the mouse buis, happens.
Quoted from Pythons.com
"Codominant - A mis-used term in the reptile world. The more correct term is incomplete dominant. It is when the heterozygous animal has a different, intermediate phenotype compared to the homozygous dominant or homozygous recessive individuals. A classic example of this is the Lesser Platinum mutation, where the heterozygous individual (Pp) is a Lesser Platinum, but the homozygous phenotype (PP) is Leucistic."
More close to how I understand it. Quoted from NationMaster Encyclopedia
"Codominance - a relationship among alleles where both alleles contribute to the phenotype of the heterozygote"