Well - If you make an image in any program like Fireworks or Paint, you can import it into DXTBmp and have all the 100% Black become transparent in SL.
The only problem is that I have a feeling grey and darker greys will be partially transparent, I am not sure and I'm about to find out.
Download DXTBmp here: http://www.mnwright.btinternet.co.uk/programs/dxtbmp.htm
Step 1: Make your image
Step 2: Open it in DXTBmp
Step 3: Click on the Aplha button on the menu, and choose Create Alpha Channel (Black)
Save it as a .tga and import it into sl.
Also - this program can be used as a converter to convert images into .TGA - or into DXT format if needed
Enjoy! I know I will!
Edit: Dark grey remains dark grey
