In Google Calendar, you're allowed to choose from a list of 11 event colors that the Google team has picked out for you - and these are the only colors that are officially supported, and can be synced between devices.
Since this list is limited to a series of very bright and saturated colors that not everyone might like, DigiCal is offering a larger list of colors.
Unfortunately, other apps won't be able to display these DigiCal colors and and these exact colors won't sync to DigiCal on other devices. If a DigiCal event color is chosen and applied on one device, it will display the closest Google Calendar event color on other devices and on the web version of Google Calendar.
Local and Exchange calendars:
On Android, the calendar provider doesn't allow you to set custom colors, so the colors you set in DigiCal won't be synchronized to other devices and possibly, other apps.