The colourful hat is finished! It reminds me of a cupcake, which is not necessarily a bad thing. I’m happy with the shape / size / fit and the striped band is great. The join is hardly even noticeable (4th yellow stripe from the left):
I’d originally planned on white diamond shapes in the main body but they wouldn’t come out symmetrical so I unravelled to triangles instead. I’m already thinking about v2 – I have a vague design in mind and some ideas on a different stitch for the main body to make it more even and with less of the rough/holy look of standard crochet stitches.