can only 1 spot of blood on the 6th day of unprotected sex be the sign of implantation??

A. if it was near to ovulation date yes it may be possible so it's better to wait and check. Implantation bleeding is never enough to fill a pad or tampon like a menstrual period. Color: Menstrual bleeding is typically a bright to dark red, and will look like what you typically experience during your monthly period. Implantation bleeding is a much lighter hue, typically a very light pink or light rust color.