As a student, working with PDFs usually involves many annotations & colours. The current UI for colours is quite clumsy:

(1) The default colour palette has very limited options & can't be customised.

(3) To use a colour outside of the default colour palette, the quickest way is to use the Properties Bar > other colour... > choose custom colour > (add to custom colours for "easier" access later) > OK.
This takes at least 4 clicks every time I want to use colours of my own preference, not including my opacity preferences.

(4) After using a custom colour & opacity, if I don't right click > make current properties default, the colour automatically changes to the last colour I used from the default palette. So I need to do this for every custom colour I use.

Suggestions:

(1) Use a colour panel similar to the ones in Illustrator & Photoshop. I look at all the available colours at one glance; & customise a colour once, then use it by clicking it once.

(2) Save favourite palettes locally / to Creative Cloud so we don't have to customise it all over again next time.

(3) Allow us to choose (as a global user preference, not every time when we want to) whether we want to continue using the last used colour & opacity (default or custom), & whether we want this behaviour when switching to another tool.