I searched online and didn’t find a clear answer (unless I’m missing some reference).
I’ve been trying this:

local redCircle='e[0;31m● e[0m'
echo "$redCircle"
RBUFFER="$redCircle"

When I echo, it does indeed print a red circle. But when I set the RBUFFER, it doesn’t.
Is this supported in zsh? If not, is there any other way to add some colours to the RBUFFER?