This bug concerns the choice of calendar colors. 

How to reproduce : 

• choose an existing calendar
• change its color
• check if the checkmark is black or white
• validate the modification
• go to an event that is affected by the modified calendar
• check if the color of the title and buttons matches the color of the check mark

In the calendar colors checkbox, the small icon indicates that the title and buttons will be black. Result: neither the title nor the buttons are black.

Normally, black check = title + black buttons white checkmark = title + white buttons and it's not the case currently.