To adjust event calendar colors, go to EDIT EVENT INFO on the event you want to modify.

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Scroll down the screen to the Event Category section. Select the color box to adjust the color and then press SAVE. 
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Optional: If you want to hard code the color all events. Use the following CSS:

/* Override calendar color for all events */
.CalEvent { background-color: #FF5E1A !important; }

Video Demo