Colors can be set as a default for a calendar or as an attribute of an individual event. If a color is set as an attribute of an event, that always overrides any default color set for a calendar.
To set a default color for a calendar, go into menu | Select Calendars and tap on the calendar to bring up a dialog where you can set the color and icon attributes for that calendar. To set a default color for a category in Pimlical's Local Calendar go into menu | Select Categories and tap on the category to bring up a dialog where you can set the color and icon attributes for that category. To set a color for an individual event, select the item in the Edit Dialog and tap on the F/B button on the right side (scroll down to see that).
Default Calendar Colors
There are two basic color schemes that can be used with Pimlical/Android, depending on the setting of the preference UseGoogleCalendarColors.
Google Color Scheme (UseGoogleCalendarColors = true)
Google Calendar only provides for a single color, not independent foreground and background colors, so in this case, the color of the calendar is taken directly from the default color associated with that calendar in Google Calendar. With some Android devices, that color turns out to be a bit too dark, while in others it may be too light, and so there is a preference: LightenGoogleColor which can be used to make the color lighter (a positive value in the range 1 to 100 sets a percentage by which it will be lighted, or a negative value in the range -2 to -100 sets a percentage by which it will be darkened. A value of 0 leaves the original color value untouched, while a value of -1 automatically makes the color darker if it is a lighter, pastel color, or leaves it alone otherwise. The default setting is -1 which usually works well on most Android devices.
With the Google Color scheme, all events in the Day and Day+ views use that color for the background, and either white or black for the foreground text (whether white or black is used is controlled by another preference: UseBlackOnColorBackground (default value is false). Timed events are displayed. In all other views, untimed events use that color as the background, and either white or black for the foreground, while timed events appear using that color for the foreground and the default background color for that view.
The Google Calendar colors are re-read any time the calendars are refreshed with Menu | Refresh calendars. Setting the preference UseGoogleCalendarColors switches to the Pimlical color scheme.
If you have a local calendar, you may want to use the Google Color Scheme with the categories in that calendar. In that case, the foreground and background colors will be set to the same value and only one color swatch appears in the Edit Calendars dialog. To set the foreground and background colors to different values, you must set the UseGooogleCalendarColors preference to false (see below).
Pimlical Color Scheme (UseGoogleCalendarColors = false)
Pimlical can set both foreground and background colors independently for events in a calendar.
Pure White (255,255,255) is considered to be the 'default' background, while Pure Black (0,0,0) is considered to be the default foreground color for text. If you want to set an explicit white or black that is not considered to be a default, just use (254,254,254) for white, and (1,1,1) for black (those are so close as to be indistinguishable to the eye).
The Pimlical color scheme does not distinguish between timed and untimed events - all events appear in the designated foreground and background colors.
Event Color Attributes
You can set the foreground and background colors for an event in the Edit Dialog (see the F/B block just to the right of the private flag setting. Any colors set there will always override the default color scheme for the calendar that the event is in.
NOTE: Not all color schemes make sense or will work on all devices. It may take some tweaking of the above preference settings to get the desired effect on your particular Android device.
Category ColorsYou can set default colors for each category or calendar by accessing menu |Select Calendar (or Select Local Calendar to change category colors) and then briefly tapping the category or calendar - a dialog appears where you can then set the default color. Note that colors set on calendars and categories are a Preference Item, not an event attribute, so they will not be synchronized across platforms. You would normally (but not necessarily) want to establish the same default color scheme for category and calendar colors on all platforms you are using.