One trick I have learned trying to capture the true colors on my Rainbow Boa's is to use either several backgrounds of different colors in a photo shoot or to use a single background that has a wide range of colors and shades within it. The digital camera, at least the ones I've used, changes the overall tinting, tone, etc.. based on the color/tone of the point it is focused on.
For example I'll use a recent picture I took which caught Navels actual coloration. This picture was taken aiming at a spot in the moss to the right of his head.

When I aimed at other points in the moss Navel looked like a big brown snake with no orange at all. Even the moss looked like it was all brownish and drying out.
But when I aimed at Navel himself he came out looking solid orange without any brown tint at all and the moss if anything was a slightly brighter shade.
A even better example is the picture series in this post by Dave Collings of several of his boas. He shows individual snakes in the same lighting and camera but on different colored backgrounds one after another. Many of them look like completely different animals just due to the background color.
http://forums.kingsnake.com/view.php?id=1540101,1540101
The advantage of a multi-color/tone background is it let's you find the target that makes the camera adjust to show a snakes true colors without having to move the snake at all.
Also another thing that makes a huge difference but I assume you already do is try both full spectrum lighting and natural(outdoors) lighting for pics.
Just an idea for the future.
Sean.
-----
1.1 BRB
1.1 Triple Het TPRS's
0.1 Silver TPRS
1.1 Amel Bloodred Corns
0.1 Abbott Okeetee Corn
0.1 Blizzard Bloodred Corn
1.1 Thayeri Kingsnakes
0.1 Reeve's Turtle
0.2 Amstaff's
1.0 Pudytat