I agree with the others, in fact it is a good thing, it means that the VFT is sucking up all the "juices"
Heck even if the trap dies (that is normal too) it's not a problem, just cut of the trap if it turns black, the plant won't feel a thing.
Hey didn't realize that flies are better, my VFTs have been munching on big ants, maybe I should give them a bit of fly from time to time
TTFN
Arvin