100%, 66%, 50% het explaination help

[Thomas Steele]

How would that work with one of the parents being 66% het?

So the 66% is just the odds of it being het. In reality it either is or it isn't. So the only real way to tell is if you produced a hypo from the pairing in which case you've then proven that the 66% het was actually a 100% het. Or you get no hypo and then you either got unlucky in the odds or it's not het hypo.

So you have two cases:
In the case of both parent's being het it's back to 66% het for the non-visual offspring.
In the case of Fire Woma not being het hypo it's 50% het (since one parent is 100% het) for the non-visuals.