When you receive an email it would be great if the Emails received in your inbox were coloured by sender. Or by Subject, or by some other means. This Outlook Tutorial video shows you how.
If you're a little too busy to see the video then try the following:
Note: Even though this above procedure is using the Email inbox as an example. The conditional formatting feature may be used with calendars as well. Using conditional formatting with calendar will allow you to change the colour of a meeting or appointment on your calendar depending on who set the meeting up, or what the meeting is about.