Photo exposure compensation

[allnu06]

Ok...I've been trying to fix this problem for a while and need some serious expertise. I have a home studio, 3 light system (2 soft boxes/strobe - monolight, 110W) and 1 strobe (40W); I use an umbrella with the 40w strobe; I use 3 backdrops (charcoal gray, black, white) and my room has white walls...I shoot with a Nikon D60 with camera settings on manual at 125/f8,9,10...my lens is Nikon 70-200 2.8 with the lens locked at 85mm...here's my proble...no matter what camera settings I use, lighting adjustment (closer, farther away, etc) my pics have a blue tent...if I increase my f/stop and decrease my shutter speed and then gets worst...on the reverse the blue tint is lessened but doesn't go away... when I check my histogram it's either slightly left or right and at one point at f/10 is was centered but had a light blue tint...CAN SOMEONE PLEASE TELL ME WHAT THE HELL IS GOING ON with the blue tint... I would very much appreciate your help...