Green Tree Pythons can be a beautiful blue. Mike Perry has an awesome solid blue female... if only...*dreams* She's even more beautiful in real life... http://market.king
snake.ca/image/1184.jpg .As mentioned Boomslangs are blue, as well as Vietnemese Blue Beauty snakes are also blue and grey. As much as I do not wish to advocate hybrids....oh man...these snakes are INSANE!!! Click <a href="http://www.corallus.com/urbanjungles/hybrids.html">here</a> to see what I mean!
They don't get much more blue than that!