How Do I Conditional Format a Date to go Red if before Today's date?

You can create a measure like this 

Colour_Date = 
VAR date_diff = DATEDIFF(TODAY(), MAX('Table'[End_Date]), DAY)
RETURN
    IF (date_diff < 0, "#C81517")

and then apply it as a conditional format to the column. The "#C81517" is HEX code so can be changed to a different red if you want

Post edited to correct table reference in the measure