Why color it, you could just paint it?

@jstane: Good suggestion. Which kind of paint would you recommend to paint those different cases:

1) Polymorph
2) 3D-printed plastic
3) ez-robot plastic
4) servo-housings

Isnt coloring much more durable and secure in regard of peeling?

Prime it with etching primer , then paint it with rustoleum or your preferred high quality paint. You will want to prime it a couple light coats to ensure it sticks well. If the surface is very smooth.hit it with 600 grit first.

Thanks Starne.
Can you please provide me with links for each product, so I can look up its specifics and thus can find a comparable product directly in Germany more easily?

Search for etching primer , and rustoleum primer.

Coloring are dye pellets your drop in the water and the thermoplastic absorbs the color but it's nothing like paint. The colors tend to be translucent unless you add lost of dye and still remind me of plastic bottles that are colored like what mountain dew and sun drop come in.

Thanks. Found it.
I think the painting part is solved. Back to topic to complete the possibilities.

Which coloring powder for Polymorph is recommended or which specific properties should it have?

@stibaer

If you want to color your Polymorph, you can mix in acrylic paint like liquitex while the Polymorph is soft and hot...Liquitex is water based and safe to work with. It doesn't change the properties of the plastic at all.

You can also use the same acrylic paint to paint on top of "cured" Polymorph since its flexible and won't crack.

Try this stuff...

http://www.mcmelectronics.com/product/21-12865?green=BFE4CF12-93C0-5CE2-0E55-BB2B397794DC

They are little pellets like the polymorph itself. You can drop one pellet in while you're heating the polymorph up. Work the colorant into the polymorph with your hands, then reheat it to shape it. One colorant pellet goes a long way. I used it to make some panels that cover the front openings in my omnibot.

www.mcmelectronics.com/product/21-12865?green=BFE4CF12-93C0-5CE2-0E55-BB2B397794DC