I agree with the suggestion. I think that there are a couple of problems.
Firstly, there are quite a few note flag icons, but all but VERY few of them
are pastel yellow, pastel green, or pastel blue. Secondly, many of them are
visually similar to one another.
I would find it helpful to have a greater variety of colors/shapes. Ideally,
I would like to be able to add icons to that list.
The great thing about OneNote is how you can set things apart from other
things visually, and I agree with the original poster that this area is
somewhat limited. Not a dealbreaker, certainly, but it is strange to select 3
relatively bland colors as your "flags."