Different contour colours for terrains making up a complex terrain?

Hi

I am looking to display the existing terrain contours as grey and the proposed terrain contours as black in a drawing sheet.  Is there any way to do this with a complex terrain composed of the proposed and existing terrains?  If not, what is recommended workflow to displaying the final combined terrain in a drawing sheet with different contour colours for proposed and existing terrains?

Thanks

Jack

(OpenRoads Designer v10.12.0.56)