Mark duplicate Timelines Google Sheets

Question

I try to mark duplicate dates in our calendar. we are two persons and each person can enter the vacations in the google sheet. The calendar is a dynamic calendar. my and his vacations have different colors (also the national holydays) now I would like to mark the holydays if we have at the same timeline/date holyday.

I have two possible solutions how could it work.

1. I just mark the date on the right side --> should be easier
2. I mark in the calendar on the left side with a third color.

here you can see that the date 07.03 - 09.03.22 is in the vacations of person B but its not clear to see it.

Hopefully someone has a good hint for me

Thanks in advance Jonas