Flapnecks vary a lot in color as they come from a wide range of habitats. It also makes it harder to know what exact humidity and temps yours will prefer. If you have the little analog humidity gauge from a pet shop don't trust it. Get a good quality electronic gauge instead. Worth the money for accuracy and sensitivity. Is this an import? She could be dark for several reasons. First, a new place and a lot of stress. Is she spending much of the day basking? If so, she may be a bit cool. If she's moving around but still dark she is stressed by stuff outside the cage such as humans or other pets. Have you tested and treated for parasites? don't trust the seller to do this. Take a fecal to a vet and have them check. There is some species info on these sites you could read for more info on color etc.
www.adcham.com, www.chamresearch.com, www.geocities.com/ccicenter, and www.chameleonjournals.com