So this isn't so much a pattern, as a color guide. I got side tracked and haven't finished my Tetris blanket--HEY A BIRD!--but I thought I'd share this simple lay out. You can totally redesign your own on some fun apps and programs like StitchSketch.
If you are not sure how to make a granny square, search YouTube, some of the best tutorials are on there, such as anything by "Crochet with Mikey/The Crochet Crowd"
I suggest making the squares of 2 simple rounds each, roughly 4 inches. Go bigger if you want a large afghan, smaller if you want a baby blanket or smaller throw.