Yellow knobs?

[mibag6]

I have a few Sherwood pieces, 2 tuners and one amp with the white faces, knobs and switches. One tuner has knobs that are quite white, the other 2 pieces have knobs that are more ivory in color. I assume that white is the proper color? Is there any way to whiten the yellowed knobs? If so, can it be done without ruining the gilt accent on the front edge of the knob?
TIA

 

[gadget73]

My S-7000 has two that are more yellowed than the rest. One is the volume, the other is the FM tuning knob. I can only assume those were the ones that got used the most. My S-5500II has all nice white knobs.

Don't know about restoring them. I simply washed mine and let it be.