ConfigurationCalenGoo has a lot of configuration options that you can find under the "Settings" button in the upper left corner and there especially under "Display and Use". You can find a list of all configuration options with a short explanation on the Configuration page.
Colors for eventsTo use different colors for your events you can use different categories/calendars (which is the recommended way, because it has some advantages) or Google's event colors. Events are usually displayed using the color of the calendar they belong to. To change the color of such a calendar just tap the blue button behind the calendar's name under "Settings", "Visibility/Download".
All-day eventsAll-day events are displayed with text on a colored background. The color of the background bar is the color of the calendar the event belongs to. The font color is white by default, but you can change it. You can change it separately for all views under
"Settings", "Display and Use", "Expert", "Day view", "Title"
"Settings", "Display and Use", "Expert", "Month view", "Font color"
"Settings", "Display and Use", "Advanced", "Week view", "Font color"
"Settings", "Display and Use", "All", "Landscape day view (week)", "Font color"
Or, if you are syncing via OAuth2, you can turn "Settings", "Display and Use", "All", "Expert/Maintenance" (at the end of the list), "Use OAuth2 font colors" on. Then CalenGoo will use the font color which is specified by Google Calendar for each calendar color (which is black for most calendar colors).