A subscriber recently wrote to me with this plaint: “Why does my calendar look like a patchwork quilt with different colors? I know it is most likely related to color categories on appointments, but why are only some of the dates shaded when I use color categories on all of the appointment?”
When you add a color category to a times appointment, the background of the appointment is shaded in Day/Week/Month view.
When you add a color category to an all day event, the entire day may or may not be shaded. What you select in the Show time as field will control the coloring.
When set to Busy, the entire day is shaded the category color. If it is a tentative event, the day is shown with category-colored crosshatching. Events marked Busy will always be purple, while Free time is not colored at all.