Did you know that you can color code items on the graphical Calendar? Specifically, you can change the color that's displayed alongside the left edge of each item. This can be done on a per-item basis.
You'll notice that the color is defaulted to Blue. When scheduling any item, simply drop down the "Color" picklist (near the bottom of the Schedule window) and select whatever color may be appropriate.
These colors are an attribute of the Calendar item itself, and are seen by all Users (even Synchronizing users).
Note: I have a few [service related] clients that use this as a mechanism for determining if an appointment could be re-scheduled or not. Red, for "do not move" and Blue (default) for "movable". This is where it really seems to shine, when you have multiple folks scheduling service techs to various locations.