Conditional Formatting on Matrix - Comparing Values per Previous Month

Hi, Mitchell92 

The dates in your original table are not consecutive, you need to create Measure 'color condition' based on a calendar table.

Please add a calendar table, replace the date fields with those in calendar table, and change ‘color condition’ as follows:

Color condition: = 
VAR _currentmonth = [Values total:]
VAR _previousmonth =
        CALCULATE (
        [Values total:],
       PREVIOUSMONTH('Calendar Table'[Date])
    )
RETURN
    IF (
        SELECTEDVALUE ( Sheet1[Date] ) = 1,
        "Black",
        IF ( _currentmonth < _previousmonth, "Green", "Red"
    )
)

Best Regards,
Community Support Team _ Eason