What is the difference between codominance and incomplete dominance?

In incomplete dominance (partial dominance), a heterozygous genotype will result in a third phenotype that is a blend of the two phenotypes. The most famous example is that of carnations. The alleles for color for carnations are R for color (red) and R' for lack of color (white). An RR flower will be red. An R'R' flower will be white but since R and R' have partial dominance, an RR' flower will produce a blend of the two parental phenotypes to create a third phenotype: pink!

Codominance and Incomplete dominance are similar in that both produce a third phenotype, different from each of the parent, in a heterozygote. BUT, the difference is that in incomplete dominance, there is a BLEND of phenotypes while in codominance, both parental phenotypes appear TOGETHER in the offspring. A good example of codominance is hair color in shorthorn cattle. These animals have two alleles for hair color: red and white. These alleles are codominant so cows with both alleles have red and white hairs on their body creating a new phenotype called roan. (Pretty awesome)