Just something easy, and with only 3 colors (in a light, medium, and dark shade)
The squares are made up in 4 different shapes: Large Square, Half Square, Large Corner Square, and Small Corner Square.
You can find the pattern at these locations:
https://www.etsy.com/listing/264308516/3-d-granny-squares-afghan-pdf-download?ref=shop_home_active_3
OR:
http://www.ravelry.com/designers/ken-jones-crochetguy