I just did a tray as my first mosaic project, too. I came here to do a search to see if I was missing anything. There is no project, it seems, that hasn't been done and posted on Craftster. Anyway, I used black grout, stained glass pieces, then painted the tray red with a varnish coating. I'll take a picture when it is dry. I distressed it with sandpaper, but next time, I'm not sure I'll do that.
One thing. . . should I use anything to seal it? I just got back from a craft store and there was a product for just that.
Here it is -
I put images underneath the clear glass tiles. I bought a mixed bag of stained glass chips from Michael's, but next time I'd like a bunch more to be clear.