I hand quilt and use many different color threads in a single quilt quite often. Doing it now as a matter of fact. I agree with the others to not do SITD. If you're taking the time to hand quilt, then let those stitches show! You'll have consistent stitches in no time. If you're wanting to do 'waves' in the water - which I think is a great idea, btw - try looking in the scrapbooking section of JoAnns or other craft stores for a wavy edge ruler. Makes that process easier and more consistent (if that's what you're looking for). Or find shapes or whatever from coloring books, etc. and just make yourself a cardboard template of the outline for your quilting design.