I will be putting down a roughly 20' x 23' bluestone multi-color natural cleft patio. I'd like to have my joints match this color: I want to use some type of polymeric sand to bind between the joints while at the same time not having a white film (or similar coating) develop while I am applying the mortar. Any suggestions? I'd like to keep the color lighter as I think it shows more of the variation in colors. Thanks.