Outlook Calendar – bright vs faded colors of appointments

Running Outlook for Mac 2011. Have tried to do an intuitive process of elimination but cannot seem to understand the following.

I have various categories color coded, but some appointments show in a bright color while othes of the same category show in a faded or pastel tone of that same color. So, for example...highly important matters have a category color of ORANGE. Some appointments so categorized show in a definitive dark orange color on the month view or week view, yet others of the same category display with a peach-tone color. Why?

Thank you....