I would not buy that nem, a white nem like that means they are unhealthy and will need quite a bit of attention to get it back to health. It looks like very bleached bubble tip though.
But how good is your water quality, nems need pristine water conditions, with no parameter swings. They also need much higher lighting than standard corals. With metal halides and T5 lighting, you want around 6 watts per gallon. More if you have PC lighting. The major concern with nems, is that if they die they can nuke the whole tank from the toxins they release, so make sure you have the water quality and lighting to sustain one, and then start with a heathy one. Even the ones that are suppose to be white, are actually a pale brown/tan color.
