|MLA Citation:||Bloomfield, Louis A. "Question 1547: Does color affect baking speed?"|
How Everything Works 26 May 2018. 26 May 2018 <http://howeverythingworks.org/print1.php?QNum=1547>.
In practice, however, most of the radiation involved in baking these desserts and letting them cool on a kitchen counter is in the infrared and it's hard to tell just what color a brownie or cake is in the infrared. It's likely that both are pretty dark when viewed in infrared light. Basically, even things that look white to your eye are often gray or black in the infrared. Thus I suspect that both the brownie and cake absorb most of the thermal radiation they receive while being baked and emit thermal radiation efficienty while they're cooling on the counter.