Option to do colour scale for whole theme, rather than just individual colours

[zoomelk]

Description

Used to be able to do this in previous version but I can't seem to find a way to get it to work now.

Why do you need this feature?

I found it really handy to see all the color scales together on one page to suss out which colour space and scales were best for all colours at once.

Additional context

Also did really like being able to change the colour space for individual colours and see how each compare within the theme - I used this to suss out the colour scales I liked best.