I actually had to Google the hidden gene Citrus, but it looks like it does some pretty cool stuff!

The impression that I get is that a lot of this so-called "hidden gene" stuff (like the "hidden-gene woma" or "hidden-gene Citrus pastel") is actually just one dominant or co-dominant mutation that was originally mistaken for something else, and mis-named, and then given the addendum "hidden gene" once it was discovered that it did something different than what it was thought to be (under the mistaken impression that it carried a 2nd, "hidden" gene).

NERD has already stated that the so-called "hidden gene" woma isn't in any way related to the "regular" woma, but Kevin thought they might've been the same when they were first imported so both were originally named "woma." Further breeding revealed that the "hidden gene" woma does a bunch of cool, crazy stuff when combined with lessers, etc., but the "regular" woma doesn't.

Based on my understanding, I don't think the "hidden gene woma" or "hidden gene Citrus" is really hiding anything more than, say, the yellowbelly or specter mutations -- all are fairly subtle single-gene mutations that just happen to do some wicked stuff when combined with the right animals. (I don't know as much about the "HG Citrus" though so I might be totally off on that one!)