Can implantation bleeding occur 16 days after sex? also what color is implantation bleeding?

Yes: Implantation bleeding rarely occurs. Having said that, yes, sometimes it does occur, but not with every pregnancy. And yes, it could happen at 16 days after sex. Implantation bleeding, like any bleeding from uterus, can be pink, red, dark red or brown. Best is to get an ultrasound about 6 weeks after the start of your last period. That will confirm pregnancy is in uterus.