Microsoft Outlook has 10 colors that you can use to color appointments and meetings. These colors are visible in Day/Week/Month view of Calendar. You can color individual or recurring appointments and meetings manually, or you can use rules to automatically color items that meet certain conditions, such as when a certain word is used in the subject or when a meeting request is sent by a certain person. Manual coloring always take precedence over automatic coloring, so if you have applied manual coloring to an item, automatic coloring will not be applied to it.
If you open another person’s calendar or a calendar stored in a public folder, you will see the colors that were assigned manually, but no automatic coloring. Automatic coloring can be seen only by the person who set it up.
Each color comes with a label. You can change these labels to make them more meaningful to you. For example, you can change the label of the color red from "important" to "urgent."
Displaying your availability status
When you view Calendar in Day or Work Week view, the pattern of the availability indicator (availability indicator: Appears to the left of a meeting or appointment (or all the way around the item when selected), indicating time status as free, tentative, busy, out of office, or no information available. Visible only in Day and Work Week view.) to the left of any appointment or meeting displays your availability status for that time period: free, tentative, busy, or out of Microsoft office.