I would thing that sugars (naturally occurring or added) or oil in the sauce could contribute to browning, in areas where it contacts the crust. With that said, yes - based on the photo, it seems like there may be a bit too much flour on the crust as well. I used to have similar problems problems, and just worked on using just *barely* enough bench flour to get the job done, without leaving too much flour on the crust. It definitely makes a difference.
__Jason