The harlequin stitch is a great technique for a project where you want to show off your crochet skills (like a baby shower or wedding gift, perhaps). While this stitch looks complicated, there are several variations that are a little easier.
This pattern uses just one crochet stitch - Treble Crochet (this is called a Double Crochet in the US). Its an incredibly simple but very effective mixed stripe using two rows of crochet for each colour. The simplicity of it.