Yellow zoas harder to grow?

[sedrostyle]

I have never had such a hard time with any zoas that had yellow in them growing.
Anyone else have this experience with yellows of any sort? Is yellow a hard color for the zoo to grow on these guys?
Also why are their some color variations that are way expensive? Just of their beauty? Or is it because they take forever to grow? Is that the deal with "rare" zoa palys being spendy ( just the growth?)