My theme seems to have disappeared. How do I get it back?

I worked on my test site today and wanted to look at a couple of different color schemes. I did not change my theme but changed the color palette a couple of times. Nevertheless, I took a break only to log on and find my theme totally gone. It shows up as my default theme but the site does not reflect it. Its white, ugly and very messy looking. What have I done and how do I fix it? Please help! Thanks so much!