This question obeys a simple law of physics. White bread reflects more radiation than black bread, precisely because it has a less dark appearance. By contrast, black bread when heated absorbs more radiation and consequently, toasts more quickly.
For those who are interested in checking this effect, we recommend doing the following culinary experiment. Prepare a dough to make white bread and add a little food coloring. Then put the dough in the oven to cook. You will see how, operating in this way, they obtain bread faster. Thus, black bread is toasted earlier than white, simply because it is darker.
