Ivory is definitely where the stripe comes from!
The pastel doesn't really wash out the yellow, actually it highlights it. I believe that the difference between the Ivory Axanthic and the Pastel Ivory Axanthic is the head. Pastel tends to blush out the head and on a "regular" pastel ivory the head is blushed out vs the dark blotchy head of an ivory. The white head on this animal to me says that it has pastel. Atleast that's the theory
Hope that helps and thanks for the compliments!