1. Sky is just his name. Puget sound garter snakes are usually blue like that, the "mutation" is the ones with red stripes.
I have a Thamnophis Radix (Midwestern garter) that is Axanthic, the green is missing yellow pigment, so it results in a blue snake.
2. Yes the baby garter was eating a fish. They all eat chopped up pinkies now.
3. common garters like Melanistic and Puget Sound snakes are around $100 each.