What I think we have here is what has become a classic debate between pizza made by pizza makers and pizza made by bread bakers. On the pizza side is someone like a Tom Lehmann who, although he is certainly familiar with the principles of bread making as a result of his perch at the AIB, does not use most such principles in his pizza making. As you know from the quoted material in Reply 440 at http://www.pizzamaking.com/forum/index.php/topic,576.msg28694.html#msg28694
, for pizza dough Tom advocates underkneading the dough and not using the gluten film test but rather a test (using an egg or walnut size piece of dough) that falls far short of a gluten film test. On the other side of the debate is someone like Peter Reinhart. Peter Reinhart spent almost his entire career on the bread side and only later ventured into pizza making in a big way. And his approach has been artisan in nature, where bread making principles like stretch and folds, preferments, autolyse and the like are incorporated into pizza making.
The reason why I asked you whether the dough after the multiple stretch and folds passed the gluten film test was to see if the dough was still on the underkneaded side, as per the advocacy of someone like Tom Lehmann, or whether the gluten was fully developed as per the advocacy of someone like Peter Reinhart. The distinction is important because the approach advocated by Tom Lehmann relies a great deal on modest up front gluten development and great reliance on biochemical gluten development of the gluten during fermentation, whereas the approach advocated by Peter Reinhart calls for full gluten development up front, in his case by multiple stretch and folds. And one of the outcomes achieved by Peter Reinhart's approach is a gluten matrix that can more effectively capture and retain the gases of fermentation. In theory, that should lead to a dough with increased volume during fermentation. Moreover, the rest periods between the stretch and folds, which are similar in certain respects to autolyse rest periods, should improve the hydration and development of the dough. All else being equal, the net result should be a greater oven spring, as well as some textural differences in the finished crumb and crust.
I don't recall ever reading anything by Tom Lehmann about using bread making principles like stretch and folds and autolyse in the context of pizza making. So, someone who comes down on the side of Tom Lehmann would say that he is making pizza and that Peter Reinhart is making bread in the shape of a pizza. I have learned that it is wise to stay out of such battles because people should be free to make their pizzas in any way that gives them pleasure and satisfaction. Tom Lehmann has spent the bulk of his career assisting mainly rank-and-file pizza professionals, where simple and straightforward procedures and economy of time and labor are important, if not a practical necessity. Peter Reinhart's methods lend themselves better to the home environment where home pizza makers can make pizzas in a more relaxed setting that might be considered more artisan in nature.
On the matter of crust coloration in relation to oven spring, I cannot recall ever reading about such a connection. That is not to say that there is no such connection, and if you tell me that the pizzas made from the doughs that were subjected to stretch and folds had more or better browning than those made using the dough hook, I would believe you. However, when I went back through this thread and looked at all of the photos for the second phase of your experiment, I did not detect a material difference in the browning of the crusts, especially on the tops of the pizzas. I also wondered whether the fact that that the pizzas all had different combination toppings might have affected the bakes, especially those with a lot of moisture-laden vegetables.
My study on how color is formed in pizza crusts has always centered on things like the denaturing of protein, caramelization of sugars, Maillard reactions, residual sugars, and pH. But, as I noted before, I have not read of any connection between oven spring and crust coloration. It would seem to me that a dough that has a fully developed gluten structure and a lot of captured gases would have insulative properties that would promote better bottom crust browning and less top browning. On that basis, I would expect more heat to pass through the dough hook pizzas to the tops of the pizzas. But, who knows? Maybe that heat helps cook the toppings and causes moisture in the dough to turn to steam that keeps the top crust from browning.