It's been a while since I've used Vision but I remember seeing some weird things with the higher bit depth images. I remember that sometimes you had to explicitly set the bit depth of the image:
http://zone.ni.com/reference/en-XX/help/370281P-01/imaqvision/imaq_image_bit_depth/
What pixel values are in your image? Could they just be really low? I'm guessing the gradient or rainbow pallets aren't helping