The best/easiest way to keep an axanthic light (outside of making a true ghost, which is hard because it's a double recessive) is to add pastel. Axanthic spiders will darken up, but a true zebra bee (axanthic pastel spider) will hold the black-and-white contrast better. Presumably a killer zebra (super pastel axanthic spider) would do even better. You could probably also add fire or vanilla, etc.
You don't want the spider because of the wobble, I assume? Nothing looks like a spider other than a spider, except maybe the woma. And womas sometimes also have a wobble.
Best bet is a pinstripe. Axanthic pinstripes also do lose their silver color as they age. Adding enchi and pastel to the mix would probably do a lot to keep the brown away. I'm not sure, I haven't see any pastel axanthic pinstripes, let alone pastel/enchi/fire/pinstripes? Are they out there?