I am in the process of fine-tuning my Hex Crystal puzzle to make it suitable for sell on Shapeways, and I have a few questions regarding what I need to go to perfect my design.

Already designed and printed two different version of the core, one was to tight to allow proper assembly, the other was so loose that it caused stability issues. To resolve this problem, I have two questions:
1. If I have a peg-in-hole style joint, what is the ideal difference between the hole's radius and the peg's radius to allow for a tight fit while still allowing the peg to rotate in the hole?
2. For a puzzle with a ball core, what should be the difference between the radius of the core itself, and the radius of the spherical cavity that the core sets in?

Also, I have started to hollow out the pieces, and so far, I have about a 20% decrease in printing cost for WSF. Considering that most of the pieces are rather blocky, should I attempt to carve out more material?

Not really relevant to the design, but does anyone know where I could get a good deal on buying multiple colors of dye to give a better finish to the next prototype?