Pattern requires 2 different coloured yarns.

From the designer:</br>

In 1992 I came up with a way to do Prime Rib circularly (in those days all my books said it could only be done flat). This was Great Fun because it is a lovely stitch and as much as I love to knit I do not love to seam. I made up a pattern for a simple hat and another one recently for a not-so-simple tea cosy and thought that was that.

Then I discovered Bicolour Brioche and thought it was gorgeous. However, the instructions I found for it were all for flat, back and forth knitting. You guessed it! My first thought was “I wonder if I can figure out how to do that circularly so I won’t have to seam?”

Indeed I could and the result of the experiment is this hat. In two contrasting colours it looks quite bold and dashing but you could also get a more subtle effect by using two colours nearer to each other in tone.

You could also experiment with stripes (if you don’t mind the idea of darning in more ends). That would easily be achieved by changing either one of the MC or CC strands or both at the same time at intervals.