For my 3 year old birthday party I did a color theme. It was a yellow party.  I started by making the invitations to look like a crayon box full of yellow crayons.  OF course at the party everything was decorated in yellow, balloons, streamers etc. We had 4 little girls. We did yellow activities such as making yellow bead necklaces, painted everyone's fingernails yellow, and looking for things that were yellow.   Everyone brought yellow wrapped gifts, wore yellow outfits, and our lunch was all in yellow. We had hotdogs with yellow mustard, pineapple, yellow lemonade, and yellow cake of course. We ended the party with yellow gift bags full of yellow surprises, such as rings, bracelets, suckers, even yellow sunglasses. I made an enlarged crayon invitation and took everyone's picture with the birthday girl, and later sent pictures with our yellow thank you notes.  It was a really fun party and all the little girls loved it.