Great idea! It is a nicely written feature request! 
When making this snippet … [Snippet] Obsidian Seasonal Header Palette … I mentioned precisely the same problem.
Levels in side Outline panels are not colored by heading level. This is a limitation of Obsidian’s tree hierarchy. If your note will have all 6 heading levels, the Outline panel will show them all in the appropriate color. If not, than top levels will be colored according to the highest level of palette and so on.
So tump up for this request! 
Cheers, Marko 