I agree that if a het has "markers" that are 100% reliable...then it's not a recessive trait, but a co-dominant one. Yellow bellies for instance...most of them look pretty "normal", especially to an untrained eye...but they do have very distinct characteristics that make it possible to tell what they are. And they do affect other morphs quite distinctly, as well.

But "markers" in the general sense, can apply without considering the animal co-dominant. They just aren't a reliable gauge. Like the belly striping on het pieds. Some have it...some don't. Some that seem to have it aren't het pieds. BUT...if you're looking at a clutch of possible hets...you know you'll key into those markers if you can.

I don't know of any reliable "markers" for het axanthics...but I DO know that sometimes (not always) they can affect another morph they have been combined with. A pastel-het-VPI may not look like a regular pastel. But, like the markers, this isn't a reliable trait to look for...and I don't remember enough about it to talk in more detail about it.