I recently created a light box to take pics of the snakes on a white background. My camera is a canon powershot sd800. The pics have been coming out great, however some of my snakes colors really pop more against a black background than a white one. When I try to go with a flat black background, it comes out grey, and totally screws up the color of the snake. I have adjusted my exposure and played with the white balance a little bit and nothing seems to help. What is the simplest way to get repeatable high quality picks on a black background?