Where do you live?

https://www.google.nl/search?q=tile+mixer&ie=utf-8&oe=utf-8&rls=org.mozilla:nl:official&client=firefox-a&gws_rd=cr&ei=msDXUvCeEM6qhQfJr4DwCw#q=mosaic+custom+glass+mixer&rls=org.mozilla:nl:official

I live in Maryland. I'll try the link. Thank you!

Narrowed down a little, I hope (google does weird stuff to locations).
But I know some manufacturing companies have a mixing option. It's often rather expensive though, so it all depends on your budget (and of course the tiles will be there for quite some time, I guess, so maybe it's worth it).

https://www.google.nl/search?q=tile+mixer&ie=utf-8&oe=utf-8&rls=org.mozilla:nl:official&client=firefox-a&gws_rd=cr&ei=msDXUvCeEM6qhQfJr4DwCw#q=mosaic+custom+glass+mixer+near+maryland&rls=org.mozilla:nl:official

If a standard blend is just a bit too boring for you, you could try buying a standard mix and a few sheets of another color. Pull some tiles off the standard sheets and when applying add the other colors in the glue bed.

That's what we are thinking of trying if we can't find an online designing tool. Thank you.

Look at Pratt and Larson in portland or