Each calendar has a color which can be configured in the calendar list.
Events within a calendar have the calendar color as default color.
For all-day events, this color is selected as the background color, for events with time setting (except in day view) as the text color. Therefore, bright colors should only be used for calendars with purely all-day events, e.g. holidays or vacations.
Some calendars offer to set event-specific colors (e.g. Google Calendars offer 12 colors, local calendars created with aCalendar offer many colors, other calendars offer only some or no colors at all).
Event-specific colors (if offered) can be set in the event editor with the color button next to the title field (please see screenshot).
With aCalendar+ other colors can also be set, even if they are not supported by the used calendar (e.g. Google or Outlook) - these colors can only be seen in aCalendar. These additional colors are offered in the color selection by clicking on 'MORE' (please see screenshot).
You can turn off per-event colors for each calendar in the calendar list. Then the calendar color will always be used, regardless of an event-specific color.
We recommend to use color-coded calendars. I.e. for each category (private, work, ...), create a new calendar and assign a calendar color, rather than manually changing colors for every event. This allows for easily changing the color of all events within a category, by changing the calendar color. The belonging of an event to a calendar / category can be selected in the event editor at the top of the editing field. Please see also: Organize your events in multiple calendars
Colors in the calendar are only shown in gray or as outline
Either the events is in the past and past events are greyed out (see Design Settings) or, if all colored text is shown in all apps as an outline font, the "high-contrast text" option is activated in the Android accessibility settings. This option is only intended for special visual impairments.