I have been doing some product shots and am having trouble getting a true white background. Im using a light tent with a light on either side ond one on top. The lights are 3500k so i tried setting my WB to 3600 and 3400k (D200 doesn't do 3500K) and the background is still not truely white, it typicaly comes out with a slight bluish or grey cast. I also tried setting WB specifically for the lighting setup in the preset mode. This still did not work. I am real close on some shots but others get a slight color cast on the background. Any ideas on how I can get a white background?