Photos aren't very good. maybe varroa mite poop.
It dosent appear to be any type of brood, foul or otherwise. It's something stored in the comb.
"Ve are too soon olt und too late schmart."- A nameless German philosopher
moldy pollen maybe?
Leer Family Honey Farm-Shannon Leer
That is very moldy pollen. Take your hive tool and scrape off the top and you'll see colored pollen below.
Not to worry.