I recently made PR's Neo-Neapolitan Pizza Dough which is perfection by the way...alas, I can not get this crust to brown.  It cooks just fine (not raw/gummy) and is chewy, crispy, flavorful,...but no color whatsoever. What am I doing wrong?

I use a pizza stone on the next to lowest/bottom rack. My oven has preheated on 450 for over an hour (scared to crank it to 500, oven is so old). When making the dough, I added an additional tablespoon of sugar. What gives????