Like Notsharp says, purpleheart has quite good moisture resistance. I use four coats of Renaissance Wax - simple to do and quite effective. Best done before assembly. Make sure you have sanded down everything to perfection first though, and don't forget to flatten the wedge and pivot areas with something like a cabinet makers rasp so the blade centres well.
Oxidising in air certainly improves the colour, but is slow. Heat on the other hand is fast and will do the same thing. Leaving them in an oven that is cooling down after cooking for a short while will do it, as will one of those hot-air guns (don't singe the wood!). You can even iron them (any heat treatment to be done before applying the wax).
Regards,
Neil