Dunno how to edit it, but:

First panel: Trick or Treat!
Second: "I-it's me, Sensei.", "Oh it's Yuzu"
Third: "Then who is this? Momoi or Midori? How..."
Fourth: "It's Momoi!"

The jokes here is that they're twins, and Momoi's Halo was hidden behind her costume. Also, her hair was split in the middle unlike usual, so the way to differentiate them is from their mouth.

I feel like the jokes works better without color since her eye color gave it out, but you can handwave it as her using contact lens.

Although the first panel dialogue already revealed who is who from the baloon text color.

cybeast said:

and Momoi's Halo was hidden behind her costume.

You can actually see all of their halos.