There is no way to know what a given mating will produce in terms of color. I know many very knowledgable breeders who have bred the same lines for generations, are familiar with all the colors that everyone has produced and still can't predict what they will get in any given litter. The best they can do is say "Well, we could get this or that color based on what's been produced before.
Color, in the partis, is a crapshoot--less so in the solids--but thats part of the fun, the surprise factor!
The best I could say would be to use a proven sire who has consistently produced roans with the type of depth and markings you like and hope for the best!