conditionally highlight column IF certain category rows has a value

Hello! I am trying to make a Gantt chart with a matrix visual. (Free Gantt charts don't meet my needs)

I need help with some DAX, if it is even possible!

I want to highlight a whole column to show when a public holiday is. So the challenge is conditionally highlighting a cell when another cell in that column is also highlighted.

I have a measure [items in period] based on this blog https://blog.gbrueckl.at/2014/12/events-in-progress-for-time-periods-in-dax/, to return a one if an item occurs on a date, based on the items start and end date.

I also have a measure to use for conditional formatting in the matrix. It colours based on if the item is on that date (2=blue in my picture) and  if it is a key date (1=orange in my picture).
 

dynamic background =

SWITCH( TRUE(),

    SELECTEDVALUE(Category[Category]) = "Key date", 1,

    [Items in period] >= 1, 2,

    99

   )

What I want to do is highlight the "Key date" in the other rows, if there is not an item in there. This the yellow (yellow =3) cells in my desired output.

Desired output

Sample data

Any ideas?