As mannaggia posted, above, Maui Gem is a branded aggregate on-site mix, available in many colors. Pyramid Cement makes this brand. There are quite a few other manufacturers of similar product, to include SGM, Florida Stucco, and CLI. All are considered excellent finishes.
In many markets, this term "Maui Gem" is used like "Xerox". Many plaster application companies have contractual agreements with specific manufacturers which offer overtly stronger warranties, because the applicators are "authorized" or "certified" by the manufacturer.
You should choose your color and feel good about Maui Gem, or any of the other major brands.