"Excess powder".

This may be the case. The color matches.
One of my frogs does not really like this powder. So when he strikes at a cricket, he'll often let it go. He'll end up getting a mouth full of powder though.
I felt so sorry for him after so many mouthfuls of powder, I gave him an undusted cricket. Dropped it next to it's head. It lasted 0.05 seconds before it was swallowed.

I find that not all of my frogs love night crawler worms. But one of them is a fiend for them and will stuff himself alarmingly with them.