I would like to play a little bit the the colour palette in Wilson theme, but it looks like the Colours and Background option does not work. When I click it (in customise mode) I see grey dot with the colour which is dominating the site, but it looks not active when I click it and there is no other button which would enable me to modify the colours. Could you please let me know, if is it even possible in this theme?
It looks like the Wilson theme doesn’t feature the option to change the background color. To change the background of this theme you would have to use the CSS. Custom changes using CSS are available on Premium and Business plans on WordPress.com. You can see the overview of plans here, https://wordpress.com/pricing/
If you don’t want to upgrade you can search for a similar theme which allows for custom colors of background. https://wordpress.com/themes/filter/custom-background