Add background colour

So I have a column added to a newsletter (with lots of empty content blocks of course but at least they don’t show on the email) and I would like to have a blue background to it.

This is the process I followed about 5 times:

1. click on the cog to the right of the section
2. click on the square beside ‘background color’
3. choose the right blue (it appears in a box with a tick over it)
4. click on ‘select’
5. click on ‘done’

The square beside ‘background color’ is now blue but the section in the email stays white.

So how am I meant to change the background colour in the emails?

{Yes, I have updated all the changes you’ve made in recent months so am on the current WP and plugin versions}