Judy,
The only things that have improved color brightness for me have been to change the angle at which I view the screen, and by choosing a different color profile in System Preferences...>Displays>Color>Display Profile: Uncheck "Show profiles for this display only," and choose a different profile, or you can also use the "Calibrate..." selection to choose a user specified profile for your screen.
You can also click on the calendar and the use the key board combination of (⌘ + I) to reveal the info pane for that calendar. Click on the calendar color drop down menu, and choose other. Then choose the color of your choice and adjust the brightness scale. You can also experiment with the three other color pallets and see if that helps.
;~)
