A bit of airbrushing on a few pixels?? ... I'm only on vol 1&2 .. is that colorized in the manga? because in black'n'white it wouldn't be obvious anyway.
Nothing like an out of context image
hmmm, I'd have drawn them with much more shocked faces in such an unexpected situation ... but then we're lacking his next frame response
((reminds me of an incident in a store about 10 years ago.... six year old girl flings her dress up in front of me and a couple of other customers and proudly announces that she has new "Hello Kitty" panties ... time stopped for all the wrong reasons and I thought her mother was going to simply start bleeding out of all her facial pores she was so red - all I could say was "I'm glad you like them."))