Pushed new branch T22088-disable-color-for-labelsetimages.

Having true synchronization would require more work than the resulting ease of use would be worth. The active label is set inside the labelset and has no connection to the node, which would require throwing events and listening to all changes of all labelsetimages and changing the color properties accordingly. On the other hand just synchronizing the color change for the active label and the color property can be done in the mapper (provided we only have one active label and do not intend to support multiple).
This however does not provide any benefit without the active label detection.