I think nearly any pattern can be assembled with a monochromatic theme. A couple of other threads active right now are talking about Yellow Brick Road quilts. It's a great beginner quilt and I've seen pics of YBR quilts in single colors that look great.
There is a quilt called Indigo something, maybe Indigo Hopscotch, that is beautiful done in all blues. She said it wasn't terribly complicated to make. Do a search and see what you think of it.
I always recommend Rail Fence for beginners, and it would also make a nice single-color quilt. Look at some of your favorite patterns. You can draw them out on graph paper and color them in with different shades of purple, or just fold and arrange some of your stash to imitate the block. Be sure to post pics of your finished quilt(s).
Darren