Uh, keep in mind that you'd have to bleach the HELL out of your hair to get a color like that (I don't know if pure white is even possible), which could very well burn your scalp and make crunchy chunks of skin fall off of your head and ooze for weeks. And you'd have visible roots after about five days and would have to dye it constantly to keep it looking neat. Your hair would be completely fried, and continued hair dyeing gets expensive fast.
Also keep in mind that most hair salons probably don't have grey dye in stock, so it's likely that you'd have to go in ahead of time so they could order it. I'm sure you could find some grey dye at a beauty supply shop, but again, you'd have to absolutely murder your hair with bleach to get it light enough before you used it.
Basically, I don't think it's realistic.