There is an extremely rare snake that is a blueish black in color, the Eastern Indigo Snake (Drymarchon coupen - meaning Lord of the Forest) these snakes are found in sandhill plant communities in the US, particularly Florida and Georgia. The Eastern Indigo Snakes are non venomous, and have an extremely docile nature which often make them popular pets.
Another common black snake is a Black Rat Snake (Pantherophis obsoletus) which can also be known as a Pilot Black Snake or just plain Black Snake, this snake is also found in the US and Canada. The Black Rat Snake has been known to grow up to 8 feet long making it the largest snake in Canada. It has bright blue eyes and is not venomous; it is a constrictor, which means it suffocates its prey then coils around them and tightens its grip until they die. They will eat anything from mice, rats, frogs and lizards to other species of snakes.
These are just a few snakes that almost fit the description, bearing in mind that if you spot a snake in your back yard it is not always that easy to get the exact coloring, depending on the light and the way the light catches the snake can actually make a color look completely different.
There are literally hundreds of snake images on the Internet and also a great deal of websites giving you descriptions and anything you need to know about snakes.
Here are a few websites of snake images and information: