Job Categories can be assigned colors which helps with identification when displayed on your history page. Below is a history page showing three jobs, each with different categories and colors. This will be most useful to identify high priority jobs, or specific categories you need to review.
These colors can be edited on the Job Categories editing screen, click the "edit" button located near any place you can assign categories to jobs. To assign a color click the colored button when updating or creating categories. If you don't want to use a color you can use the checkbox for "No Color" if you prefer not to use colors with categories.