D&R:

I too have heard the stories of purpleheart staying purple. I think
every wood from South America has several different types of the
species, and this probably is no exception. I have actually seen
purpleheart go to a dark, brownish purple over a period of years when
left outside (small piece on the burn pile). It was beautiful.

OTOH, I have friends that have used it, kept it out of direct light,
don't have the work directly under a lamp, and used UV resistant
exterior urethane on their interior piece. It turned a beautiful dark
brown, but with no character at all since the wood was without defects.
So it was stunning in purple, and just pretty in brown.

I think "you pays your money and takes your chances" with this wood. I
know from our local exotic lumber supplier that half the time he is
selling something that comes from South America he doesn't know exactly
where it came from, if the wood came from the same stand, forest, or
country. It is the same with all exotics, since down there these are
also know as firewood to many of the indigenous people.

That being said, I used laquer thinned by 1/3 and a spot of BLO in it
to finish all the purpleheart beads and pendants for my niece's
Christmas presents. Turned out great and finished easily.

Good luck!

Robert