True. I am not sure exactly what hash is being used (though others seem to indicate md5)
I have heard from colleagues in the past that consumers of illegal pornography used to (or possibly still do) commonly apply a negative filter or hue shift to images to avoid hash matches and flesh tone detection. This helps when combined with other stuff if someone scans their disk or they get raided and have too much stuff for law enforcement to look through properly. They then set up their screen or display settings to counteract the filter when viewing it.
Thankfully I have no experience with illegal pornography and definitely don't want to gain any, so hopefully I will never be able to confirm that firsthand.