Thank you for your reply Natalia.
It would be great if Nancy could interact directly since this is her area of expertise.
I assume Shapeways is using 3DSystems Duraform Flex material, infiltrated with Flex Seal 2-part urethane. While it is true that Flex Seal is only available in Black, Red, Yellow, Blue, and Natural White, the spec sheet says they can be mixed to create custom colors. Take a look at the brochure here:
https://www.rpc.msoe.edu/datasheets/sls/Duraform_Flex.pdf
Just to make things super easy for you all I've attached the brochure and a embedded a screenshot with the relevant information.
The material comes in 1kg cans, and I'm sure Shapeways will go through a lot of it if they offer it in a useful color. Simply mixing 3 cans of white with each can of black would give you a material that is actually useful for end-use products.
Just my two cents as one of your customers.