How is incomplete dominance different from codominance?
Certainly if you are talking about signals, red, white, and pink phenotypes are distinguishable rather than intermediates...

But inheriting a character is far away from the concept of distinguishing signals. As genotype of an organism decides its phenotype, you should know that in a hybrid both the paternal and maternal traits would exist. If one is dominant then it is expressed and the recessive is not.

However if the dominant gene is unable to express itself independently in presence of the recessive and if the recessive is partially expressed, then both the dominant and recessive give rise to an intermediate phenotype which "only one of them cannot produce"

This is what we call blending. In case of Snapdragons, pink is a phenotype that allele responsible for red or white alone could not have produced.

In case of co dominance you can notice multiple dominance. i.e., no recessive character is there. All alleles are expressed "independently of one another" in an organism.

Eg:- AB blood group.

Also consider cross between black coat coloured cat and white cat. The offspring produced has black and white patched coat colour. i.e., Black and white didnt blend to give rise to grey. I mean, alleles responsible for these traits are independently expressed.

Hope that clears your doubt. :-)