Hey
squawk, man that's a beauty!
I can make out a bit of discoloration on the neck pup, but it doesn't seem offensive to me.
Part of the charm and mojo of old white plastic bits is that they do tend to go creamy over time. So much so, that God made
creme plastic bits as standard factory items so we won't have to wait
If you feel some driven desire to whiten these pups, first of all, reconsider
You might have a shot at the mounting ring, but anything you try with the pups is going to be potentially damaging to either the plastic itself or the electro-magnets.
There are number of methods which purport to whiten plastic but I would think long and hard about any of them. Many involve soaking in liquids, so right away you're in trouble unless you up for completely dismantling the pups (not a good idea). From what I understand, hydrogen peroxide together with an 'oxy' cleaner works on ABS plastics, but again, you need to immerse the plastic part; and I don't know for certain if the pup is ABS or PVC. As a general rule, what you should avoid at all costs is bleach! This will brighten things up but usually at the expense of deteriorating the plastic over time.
Perhaps the easiest and safest approach is simple gentle abrasion. Try using a fine sandpaper #2000 or better. With patience you can remove the yellowed top surface and expose some 'fresh' white plastic. Ordinarily you would 'wet' sand but...
The added benefit is that your poles will get nice and shiny too! Use a compressed air canister to blow away the debris, then polish the surface with a little liquid polish.
Good luck!