We have a user who is using Oulook 2010. He assings colors to calendar items he creates. When someone sends him a calendar appointment, he assigns it a color as well. Anywhere from immediately to about 5 minutes, the color changes on its own to a lighter version of the assigned color. For example, he assigns an appointment to red and it's changed to the lighter red color.
His colors do not change when he creates appointments for himself. The colors do change when someone else sends him a calendar invite, from both inside and outside the organization.