Paul, this is a feature that I first requested a year ago and it's still not yet there in terms of priority for Bubble. Which is fine, because I did end up finding a workaround!
You can store hex values as a database text thing, and call them back later in HTML and Text elements after [color=#DYNAMIC HEX][/color].
So in one of my apps, I am creating lots of HTML blocks where dynamic color will be used instead of relying on the default Bubble Text or Button elements. Once I started doing this via reusable elements, the speed and time to implement such dynamic data doesn't take up any more time than if I were to be using the built in elements. Now that we have access to JS plugin-side building, I bet you could find a way to do this with a custom plugin as well.