Adjust the text color depending the color of entry in the calendar view

Steps to reproduce:
1. Create a new calendar
2. Select a color from "Colors of entries in the calendar view" (i.e. "#FFFFFF")
3. Save & view
4. Create a new event
5. The writing is not visible, because you selected a very light color (i.e. "#FFFFFF" from "Colors of entries in the calendar view") and the default color for text is white.