let me get this straight, there is no lighting whatsoever on this tank ? none at all? Mushrooms are a lees light demanding coral, but nevertheless, their only energy source comes form the zooxanthellae that they harbor inside their tissue. these litle guys are what need light to produce energy for the mushroom to grow. if htey have no lights on their tank, then they might just be bleached out. i agree with blennybabe that there are some white shrooms out there but even these tend to have a slight hue to them, whether it be blue, or green , etc. like i said before, i have shrroms that fall into crevices, adn turn white to almost transparetn, but still hang on because they get a very marginal amont of light somehow. i woud pass on them, or ask them to drop it in price cause you think they are bleached, get em for cheap and put em in your tnak, and see wat happens. they migh tcome back beautifully, who knows!
good luck
jon