So there will be a future update in which mixing more than one graphic set will be possible.
How then will this affect the color change in the skill panel color and info panel font, since the colors of those are affected by the chosen color of the minimap/bridges of a graphic set?
The exact details will be decided closer to implementing it, but essentially, you should think of it not as "the level has more than one graphic set", but "the level has one graphic set, with the ability to also use pieces from other ones". Or alternatively, "the level has a primary graphic set which decides bridge color, etc, but can use pieces from any set".