I'm not sure how good of an option it is but I've heard of people "baking" wood in direct(ish) sunlight over time to speed up the process of coloring. I've never done this before though and I try to keep my instruments away from the sun as much as possible.
If you do have a refinish job you could always have the painter put a little yellow tint into the finish. I had a reissue bass by Fender and it had yellow tint in the neck finish. Maybe a replacement neck would be the simplest choice.
I'm not a giant fan of straight white maple myself so for my latest "non-bass-stringed-instrument" project I've applied some walnut pore filler directly to the wood. It's filling the gaps in the wenge and coloring the maple in one step. I wanted more of a vintage violin type of finish that that's how it's turning out. You'd probably do better with the yellow tint if you're looking for that old Fender neck look though.
Before and after:
