I know there is a blue stripe garter snake, but I am not sure if that is the one you are referring to. Is this it www.uga.edu
If it is not the gater I know that black racers when they are young are a dark color with blue stripes on them and have a white chin try looking it up on google.. I hope I could help. Good luck
Both the Garter Snake and the closely-related Western Ribbon Snake has a blue color phase, with stripes running length-wise down the body. Both typically have a light-colored spot on top of the head, too, so it's a pretty safe bet this is what you saw.
I don't really care