When working on FlexCalendarFX I got to the point where I had to define a set of colors to visualize the controls for different calendars in different colors. And not just one color per calendar but several: a background and a text color for deselected / selected / hover states.
The colors were used in several places but for the sake of brevity I only focus on the visual calendar entries in the day view of FlexCalendarFX. The two screenshots below show the same entry, first deselected, then selected.