Suggest you will be best served by choosing the shop you want to do the work as your next step. Then work with them to find colors available in the powder brand(s) they like to use.
Powder isn't like wet paint - they can't mix a color to your spec (unless you want to pay an extraordinary fee) - you'll be presented with finite number of color samples to select from. There's usually lots more than one "black" and lots more than one "red", and frequently there's a range of 'gloss' factors for each color.
Final selection should be made from actual PC samples, thin aluminum 'coupons' with the actual finish color and gloss you choose. These are like carpet swatches in the PC industry - if the shop only shows you paper catalog 'color chips' for final selection, your alarms should go off. The gloss factor can hugely affect the way the color looks so be sure you are looking at exactly what you will get on your final product.
Two-tone PC is tricky, often involving partial curing and/or hand teasing of edges. If you go that route I strongly suggest you require the coater to show you a test with the specific colors you want; bleed-thru and fuzzy-edges between colors can easily happen and you don't want to be surprised in a bad way with the resuling effect
Paying for a test may be required but if you want anything that is out of the ordinary (single color per piece) you need to pay for the special service
Many reputable shops that do very good monotone coating simply won't consider two-tone at all because the results are too unpredictable and labor intensive. Those that will undertake it treat it as a premium service with a cost structure that reflects the effort and risk
Think about the process of spraying a fine powder on a static-charged surface then melting the stuff so it flows together. By definition the cure involves the powder flowing. Now imagine how to do that twice without things blending or beeding in some way ..... you can start to see the challenges in doing two-tone PC with crisp edges between colors
.
Unfortunately there's lots of newbies in the PC biz that 'sell' beyond what they can actually deliver. Look for a shop that's been in biz for awhile, and if you ask for anything other than monotone, demand a sample of the finished effect (and be willing to pay for it).
Good luck!