I have experience in getting high-end plastic boxes manufactured (some in US, and increasingly in China because of price dynamics). Believe me, it is not a big deal. The variations are all commodity - you may have to get different molds made and finish made, but they will work will all different types of plastics. The plastics are already colored when in the pellet form (i.e., you dont paint on them) so colors variations are trivial to achieve.