The following approach works well for columns where you want to use 2 colors, and there are 2 distinct options in the column (such as Yes \ No or Existing \ New).
Set the first color by applying shading to the entire column:
Then you can assign the conditional formatting to the same column. Conditional formatting always overstrikes cell formatting, so with this approach you can use a combination of 2 colors:
Don’t forget to check ‘Show conditional format on sheets’ if you wish to display \ print the colors. This feature was also added for Revit 2014.