Several asked about the colored 4 x 4 tiles sent out in my tesserae exchange box, so I decided to see if I had kept any information about where I got them at the SAMA conference in Phoenix. And guess what!
They are called "Thin Brites" and they come from Holland. I purchased them from "Mosaic Studio Supply" from Oakland, Ca. Their web site is www.mosaicstudiosupply.com and you can order online.
Hope this helps!