It's not really that my shade of blue is special as such, although I'm very partial to it and it's a hard one to work on, but more so the way I go about colouring that makes it so nice, most people try to put it over yellow hair and that makes it ugly XD It's an expensive and very time consuming process to prepare the hair for a colour like blue, it needs to be as near to white as possible and the darker your hair starts the harder that is. I have actually already answered this very question in detail on my deviantart account, as it's a detailed account of things you need to do and has a range of colours featured etc,
I highly recommend you read it, as it's better than me regurgitating the same explanation over and over and it has photos etc,
www.clefairykid.deviantart.com c: There's a FAQ button on my profile and that'l lead you to the hair FAQ.