I got a solution to make the rest of the cells blank if they do not have a date or value in them.
Make a new rule. Select rule type: Format only cells that contain"
Choose "Format only cells with: Blanks:"
Then format it with a white background, or color of your excel spreadsheet. That should make all blanks turn white. Leaving the other dates that are over 30 days stay red. 

It doesn't work well, only the cell L1 is formated and no other one. Only the cell L1 is marked with an other backround color. Pleas add also when and which cells should be marked before clicking on "new rule."

The issue with less than 30 days is, it is even high

lighting blank cells.

Hi there, I've searched far and low and have not yet found the specific formatting that I'm looking for. I would like to be able to have a list of all the 5th Sundays in the month, per specific year(There are always 4 months that have 5 Sundays every year).

So since I don't know how to do that, I have a function that looks at dates (Jan - Dec of a year) and finds the first Sunday of the month, then adds 4 weeks to that, which would give me the 5th Sunday of the month.

=DATE(YEAR(A2),MONTH(A2),1+((5-(1>=WEEKDAY(DATE(YEAR(A2),MONTH(A2),1))))*7)+(1-WEEKDAY(DATE(YEAR(A2),MONTH(A2),1))))

So some months the resulting dates actually show up in the next month - well all of the ones that don't have 5 Sundays.
So now I was thinking if I could at least have conditional formatting where the "DAY" value in the date is above a certain number, then I could at least easily highlight the ones that have 5 Sundays. But I have not been able to figure it out. Can someone help me with that? It seems to me it should be simple to have a conditional formatting that highlights all the days that are after the middle of the month, regardless of which month or year it is.

I am using the Highlighting function with dates greater than 90 days, but then I have a completed date that I would like to use that will remove the highlight when a date is added to this cell. Example Due Date - Highlighted Cell - Completed Date. Is there a formula that will do this?

Is it possible to compare 2 dates like; (first date > (second date+5)), and condition a cell colour based on the result?

I got the above down but what if I only wanted to count weekdays? No weekends or holidays.