Check out these Kona whites at Hancock's of Paducah:
http://www.hancocks-paducah.com/Item...White--srcin-1
The PFD has optical whiteners added to it, which makes it more white. However, what I am thinking is that the second piece may be muslin white while the first piece might be a Kona cotton solid white. They are both white and both cotton, but the fabric is woven differently (I think) and therefore may reflect light differently.