I don't think the heterzygous BP will make a better looking axanthic if it was a lighter colored normal. It may change how much the snake browns out in the future (such as how dark the snake actually gets), but that's where the different lines come in (like VPI). So, I don't believe the color of the normal has anything to do with it, but the certain line of axanthic and how well the axanthic kept its colors when you bred it to make the hets.
What I've heard, you breed crap you get crap, and that's true for the most part LOL.