Having just referenced a diagram from another system, it was a good reminder that charts are abstractions that might be unfamiliar. So a Legend is often useful.
The Contextual Family Tree from GEPS 30 New Visualization Techniques
Gramps has titles but no legends, no color keys.
It would be nice if charts had the option to insert a (collapsible?) legend as an inset box.
And while that Contextual Family legend is comprehensive, the thought occurred that having the legend diagram a selected person in the tree instead of a dummy could open new options and or use more familiar data.