How old is it exactly? If it's less than 7 working days since you received it there's the distance selling regulations. If it's over that then you can try phoning Viewsonic, they make take pitty on you, but in theory they won't change it for one dead sub pixel. However if you don't tell them it's a subpixel (which it probably is, but you'll know better than me about that) and just say pixel (they don't know whether you know the difference) they may change it.
There's a couple of programs you can run to try to kick the pixel/subpixel back into life, but someone else will have to post the links to those. That should be the first thing you try.