I have screened bottom boards and noticed on the plastic pull out sheet (the one that gets sprayed with Pam oil) a few maybe 3 SHB larva. Most of the sheet was covered in small yellow bits, like crumbs of comb I guess. Is that normal or is that the result of the larva boring and chewing up the comb? I didn't see any actual beetles on the sheet or in the hive during inspection.
The white and yellow stuff is most probably cappings, the red dots most likely mites, the SHB larva were probably ejected by the bees. A few SHB in a hive can be harder to find than an unmarked queen.