Monte...
Try that black pearl in plain clear plastic. Could prove interesting and you can always tone things up with the black colorant if that goes south. It looks as though the black colorant masks what the black pearl can do. I'd even try a thin purple or thin blue with the black pearl, but go light on how much you add at first.
I have a bunch of glitters from Caney Creek in the medium grade and love the stuff Jason offers. One color of glitter that I absolutely love to use in various transparent plastic colors is fucia. Its not red, its not pink, its not purple, but it goes into blue, purple, red, pink, clear plastic very nicely, but its hard to find outside of HL or Michaels.
I haven't seen any bleeding issues yet with any of whoever's glitters I am using and I do a lot of remelts. I guess in using glitters not sold specifically as ones to use in the plastics production this problem might come up in time.