Of course it wasn't enough to just have a white tray, I mean - that's boring! So I took some white poster board and using water colours painted it seaside colours. Yes, it is taped to the table. My table gets a beating with all the projects it has to live through so I figure why stop now. The paper is still a bit wavy, but as it dries it flattens out. I have zero patience and so I used a hair dryer to speed things up a bit.
Then using a paper cutter I cut it into
stupidly small half inch squares. If you are going to try this at home, I would strongly suggest using a square punch, as it's almost impossible to get perfect squares otherwise. Using Mod Podge I glued each square down. Weeks later I finished it by sealing in the squares with a coat of Mod Podge.
It took forever to get the squares glued on. I went with paper because I thought it would be faster. I'm thinking it might have been faster to use real tiles!