You’ll need minimum 2 colours of DK yarn. Make sure they have good contrast so you can see the pattern.
I used stash scraps - and ran out of green, which is why I have 2 background colours. Use as many as you like!

For an adult size hat use thicker yarn on larger needles. Eg. I used 3.75mm and 4.25mm with aran weight to make an adult small-medium hat.