Material Theme Builder

Hi,
I’m trying to use the Material Theme Builder. When I click the button labelled ‘Custom’ the panel below displays Primary, Secondary, Tertiary & Neutral colours. However, clicking on them doesn’t do anything - I was expecting to see a colour picker. The button display also looks a bit off (coloured blocks over greyed out circles, see attached).
Any idea how to set these colours for a non-dynamic M3 set-up please?
Ewan