[FEATURE] Add custom callout colours

[charliedodds]

Is this a unique feature?

• [X] I have checked "open" AND "closed" issues and this is not a duplicate

Is your feature request related to a problem/unavailable functionality? Please describe.

I need to be able to completely customise callout background and text/border colour

Proposed Solution

Add colour pickers to the callout option menu

Screenshots

before

after

Do you want to work on this issue?

Yes

If "yes" to the above, please explain how you would technically implement this (issue will not be assigned if this is skipped)

add colour picker options to current callout block options