You can change the color of contacts in BusyContacts using Address Book colors or Tag colors.

You may change the color of an address book and all the contacts on that address book by control-clicking on it and choosing a color, or double-clicking on it to open the Address Book Info dialog.

You can also use Tags to color individual contacts, by control-clicking on a Tag in the Tag List and choosing a color from the Color submenu.

By default, contacts appear in the same color as the Address Book they are stored on. But Tag colors take precedence over Address Book colors. So, if you colorize a Tag, any contacts assigned to that Tag will be displayed in the Tag color rather than the Address Book color.

For example, lets say your iCloud Address Book color is blue, so all of your contacts on iCloud appear in blue. If you create an 'urgent' Tag and color it red, any contacts assigned to the 'urgent' Tag will appear in red instead of blue, because Tag colors take precedence over Address Book colors.

If you add multiple colored Tags to a contact, the color of the first Tag sorted alphabetically will take precedence. So, if you have a 'family' Tag colored green and an 'urgent' Tag colored red, a contact assigned to both Tags will appear in green, because 'family' is sorted before 'urgent' alphabetically.

Note: Tag colors are Mac specific. If you have an iMac and a MacBook Pro both running BusyContacts, the Tag colors you set on your iMac will not sync to your MacBook Pro. The Tags themselves will sync, but the colors of the Tags must be configured separately on each Mac.