My sons (half asian) both have what looks to be huge grey blue bruises on their bums and lower back. My older one's have faded considerably but my baby looks like he's been hit very hard on the bum!! I feel the need to always explain the birthmarks whenever someone sees them (changing him in front of friends, for his 1 yr photo shoot, etc) so they don't think horrible things!! I didn't know about these marks until I had babies with them either!