Make your own colorful capital letters to display on the wall. All you need is some paper (I used colored construction paper), some glue (any non-toxic glue will do), safety scissors and poster paints (I used Crayola "Washable Kids Paint") which can all be bought at a Dollar-Store or (with coupons!) at a craft store such as Jo-Ann's or Michaels.
If you have a color printer, and you want to save some time and mess, print the "Pre-colored" version. That way, all you have to decorate is the piece of paper/construction paper that will be the base/frame for your cut-out creation. (This is what I did for the photos.)
But if you want to really go for it, print the Ready-To-Color version and color everything in your own custom colors.