Only attempt if you are comfortable knitting two colour brioche in the round - plenty of good YouTube videos out there to help with that.

Pick two contrasting colours to make the hat really pop

The decreases are fiddly and take patience. Make sure you have knitted all the stitches together before you pull them off your needle.

When casting on, you want stretch. To do this I recommend holding a second needle next to your cast on needle to give your cast on stitches some extra yarn. Using a second needle of the same size gives enough ease in the brim.