Seems to be a color depth thing. I copied each one to the clipboard ("open in default editor" doesn't work for me, Photoshop says the file could not be found), pasted into photoshop, changed mode to RGB, copied, replace from clipboard, and now they look fine.
Weird that none of my other sprites (all imported from GIFs) got messed up in the import.
Weird that none of my other sprites (all imported from GIFs) got messed up in the import.