Breeding a pastel to a pastel will throw 50% super pastels, hence the codom. Pin x pin will only produce more pins and normals. Co-doms have a super form. Mojos, lessers, butters, womas, pastels, yellow bellies, phantoms, fires, etc. all have super forms so they are co-doms. Spiders and pinstripes don't have a visual super form, so they are dominant. You can think of co-doms as visual hets for the super forms, ie. lessers are hets for BELs, and since you can visually tell a lucy from a normal it's a co-dom.