A co dom gene will give you a visual expression with only one gene, but also has a super that appears when that certain gene is on both of the alleles.

Example-

A pastel has x gene to make it a pastel. It is bred to another pastel with x gene that makes it a pastel and they produce a super pastel with the x gene from both parents making it XX.

From here, every offspring that is produced by that super pastel will contain at least one of those x genes, much like a visual recessive will throw at least hets.

Hope this helped.