You can add a color label to the calendar text. Follow these steps:
1.Click the calendar button for Outlook 2003.
2. Click on Edit menu, select Label, and then chose Edit lables.
3.Edit the label text as required.
If you want to assign a label, create an appointment. From the Untitled-Appointment dialog, click the label drop-down arrow. Choose the desired label from the list. You can also, right click on a calendar item and choose the label from the menu.