From the designer:
Like many sock knitters, I have a large stash of multicolored yarns that do not play well with elaborate patterns. This pattern was specifically designed with gradient and self-striping yarn in mind: it does not interrupt the color sequence at the heel. In fact, this is the easiest heel you will ever knit - all the magic happens at the cuff and toe, and everything in between is smooth sailing.
The concept was inspired by the shape of a miter joint, a simple method for joining two pieces to form a corner, commonly used for picture frames. I inserted a 45-degree heel section and a gusset on the instep to make the sock less angular and more foot-shaped. The miter joint is not very strong, but don’t worry, these socks are highly unlikely to snap in two!"