I have created a small program to design a dice sets to be used in Virtual Mat. It has immediate preview of the color/texture changes, so you can experiment with various settings quite easily.
It is a standalone jar (no webstart for now, sorry), you can download it here dicedesign-0.2.jar and just doubleclick on it after the download. You will need java 6 installed for it to run properly, you can get it from Java site in the case you don't have it.
You will be presented with few windows - attributes, color chooser and preview window. Color chooser is not usable at start - you need to click on any attribute and then color chooser will start controlling that attribute. After that, chose different attribute, play with colors and so on.
To control preview area use following keys - AWSD to move around, QE to rotate, RF to tilt, ZX to zoom in/out. You can also use mouse to kick dice around, but if you get them too far, you will need to restart the application.
To see the example dice set, download magma.dicedesign and use 'Load...' from dice designer menu. If you manage to create something nice you would like to share, save it and let me know - I might create a repository of best looking dice sets.
Hint - if you want to get rid of glow after enabling it, change glow color to complete black.
Program might be not running on some older graphic cards or integrated Intel chipsets. Anything from Nvidia or ATI/AMD produced in last 10 years should be enough to get it running.
Please make sure you save it to the disk and run from there. When running directly from Firefox download window, there is a problem with unpacking some libraries, which cause the preview window to not appear (you should get 3 windows, one of the showing the dice on the table). When running from windows explorer, there should be no problem.