abc and Wally,
Your recent experiences with the light crust coloration from using the All Trumps flour prompted me to research the All Trumps and KASL flours to see if I could find an explanation for the difference, particularly when the two dough formulations were otherwise the same. I looked at the specs at the General Mills and King Arthur websites and discovered that the two flours are very close in almost all respects except that the KASL seems to have less barley malt and it has a higher falling number (FN) than the All Trumps. The FN is an indication of the amylase enzyme performance of a given flour by which natural sugars are extracted from the damaged starch in the flour by enzyme activity. The FN number is low when there is a significant amount of amylase enzyme performance and high when there is a low level of amylase enzyme performance. The FN for the KASL is 250 +/- 30 sec., and for the All Trumps it is 200-240.
Before assessing the significance of the different falling numbers of the two flours, it may be helpful to consider what factors govern crust coloration. The two main sources of crust color are caramelization of residual sugars in the dough at the time of baking, and the Maillard reactions. Residual sugar is that sugar that is in the dough and at the surface of the unbaked crust at the time of baking. It is sugar that the yeast has not consumed. As with any sugar, as the temperature of the pizza rises during baking, the surface sugars caramelize. They get darker with time, just as melting common table sugar in a bit of water on the stove becomes darker the longer it is cooked. The Maillard reactions are reactions that take place between reducing sugars (also residual), protein (amino acids) and moisture. The more sugar there is, or the more protein there is, the greater the degree of crust coloration, and it will intensify with increasing crust temperature. If the All Trumps finished crust has a light color, to me this suggests that there may be insufficient residual sugars in the dough at the time of baking. Since the two flours have very close protein contents, the Maillard reactions are most likely quite similar and not per se responsible for the lighter crust color.
If the above analysis is correct, then it is quite possible that the All Trumps flour is subject to a shorter fermentation window than the King Arthur flour. The lower FN for the All Trumps flour seems consistent with this assessment and suggests that a shorter fermentation time should be used for the All Trumps than the KASL. To compensate, it may be possible to add some diastatic malt to the All Trumps to increase the amylase enzyme performance and thereby help extract more sugars from the damaged starch in the All Trumps flour so that more of it is present in the dough at the time of baking to contribute to crust coloration. It may also be possible to add ordinary sugar or possibly barley malt syrup (nondiastatic) to the dough to accomplish much the same result, although one has to be careful not to use too much because of the potential of the bottom crust prematurely browning when the pizza is baked on a hot stone. If diastatic malt is use, the recommended rate is about 0.5-1.0% of the weight of formula flour. Above that, there is the potential of the dough becoming gummy and the finished crust may have a reddish color. A common brand of diastatic malt is Bob's Red Mill.