How does the term codominant describe the action of genes in an incomplete dominance trait?

 Codominant genes are both expressed at the same time if present in an organism. For example, if a person inherits a gene for type A antigen from one parent and a gene for type B from the other parent, that person will have type AB blood. In this case, both the genes for antigen A and B are expressed and the person will have both the A and B proteins present in their blood. 

However, in incomplete dominance, the two genes "blend together" to form a different phenotype. For instance, in Japanese four oclock flowers, the gene to produce the color Red (R) and the color white(W) are both equally strong. Therefore, if a plant inherits a genotype of RW, this plant will not be red, nor white, but instead, a blending will  occur, producing pink.