Event selection feature (works in DayPilotCalendar) could be helpful. You can activate it by setting EventClickHandling property to Select.
By default, the selected event is emphasized using enhanced top and bottom borders. If you use EventSelectHandling="CallBack" and handle EventSelect event on the server-side you will be able to use a special background color for all parts of the event (upon clicking).
For the mouseover functionality, it would be a bit trickier (and might require some changes in the code of the control) but it would be possible as well. Let me know if you are interested in that option.
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