Getting back to understanding genetics, I've been re-reading
Storey's Guide to Raising Ducks by Dave Holderread, and would highly recommend it as a sort of "primer" for anyone interested in figuring out genetics. True, it's not about peafowl, but the author does a wonderful job of explaining how the various mutations work, alone and with others, to result in the phenotypes of various duck breeds.
After describing the various breeds and the colors/patterns they display, in a further chapter on genetics he lays out which mutations are responsible, how they're inherited, etc. That basic knowledge can translate easily into peafowl. All you'd have to do is lay out the individual mutations in peafowl and how they are inherited -- Incompletely Dominant (White, Pied, White Eyed), Autosomal Recessive (Blackshoulder, Midnight, Bronze, Opal, Charcoal, etc.) and Sex-Linked Recessive (Purple, Cameo, etc.). Then see how mutations inherited the same way are presented for ducks. While we don't have all the same specific mutations, and appearances will thus differ, how they are passed down in breeding will be the same.
The next step would be in learning what peafowl would look like with these various genotypes. What is the visual difference, for example, between peas with no White Eye, one copy of White Eye, and two copies of White eye? What about the Pied gene -- Normal vs Split to Pied vs Dark Pied? When you understand how a genotype will look (i.e. its phenotype), then you can work in the reverse direction -- by looking at your birds, you can try to figure out their genotypes. For things you can't see (i.e. being split to Autosomal or Sex-Linked Recessive mutations), you'll have to know about their parents, or conduct test-breeding. But once you can assemble and record the genotypes of your peas, and after understanding how the genes are inherited, you can then answer your own "what do I get if...?" questions.
ETA -- if the section "Understanding Duck Colors" on Mallard-derived breeds is too complicated (because there are so many mutations), skip to the section on Muscovies, since there aren't as many mutations in that species.