collor 2 or 3 cells in a week

[glda19]

in the file i set de color cell yello en green cel by hand.

In the year 2020 the yello

[AliGW]

I have looked - no idea what your logic is, sorry.

[glda19]

I have manual collor the hollidays when a person works half time.
One week he works 3 days the other week he works 2days

I want that de user can select the days in 3 cells the days that he not work. Then collor the cells that he is not at work. In 2020 he have to work 3 days in week 1 en 2 workingdays in week two.
What i alredy found is where here are 53 weeks in a year the 3 days work week are in the oneven weeknr. And by 52 weeks thy are in the even weeks.
What is the formula of function to detect that
3 days work in the even or oneven weeks are so that the 2days work week in the other week and then collerd 2 ore 3 cells for not working