Just like it is possible to define once their custom sort order, it would be really useful to attribute once the custom colors of single values of categorical properties.
I know it is possible to "borrow" the colors from another visualization but:
you have to do it, while it would be possible no to
it does not work if your color by property is set on-demand via a property and a control in a Text Area
note: I also know about the Document Coloring Scheme but it still feels more complicated than it could be