Offer the plate in stainless steel and aluminum
Offer the plate in the "standard" size, and this will work for most divers, but also in "Tall" and "Small" sizes for divers who are extremely tall or short.
Consider a slight "bend" in the lower corners, a few degrees away from the divers back. Usually not needed, but sometimes can help prevent the lower corners "digging" into the lower back of some divers.
By "colors" I assume you mean for anodized aluminum plates?? I would stay away from any type of "paint" that could scratch...
De-burr all edges. Don't make the diver do that, unless the plate is sold at a very discounted price.
And, select a price point that makes you VERY competitive with all the other fine plates out there.
Good luck with your project!
Best wishes.