I was lucky enough to find all my Opals last year at the Dollar Tree. I'm missing 08: Violet Opal, but other than that, I think I have a full set of them. The Opals are very sheer and are meant for layering. Each color on the wheel is layered over Black. Most of these are untried (yikes) and I listed some of my favorites:
Make sure to click the picks to enlarge them:
Crystal Opal is a great duochrome, it flashes purple and green:
Pale Pink Opal flashes pink and blue. I love how Red Opal is actually green! LOL:
Earthen Opal is red and purple - so cool:
Flame Opal is another red/purple combo, but not as dramatic as Earthen Opal:
Thanks for looking!