Gravid color change

[Vivid-Dawn]

My guppy is about 3 weeks pregnant. This morning, I noticed her gravid spot was translucent orange. Now, 45 minutes later, it seems to be going back to black. Is this normal? I know that Neon Tetras will get "washed out" at night, and after the lights have been on for a few minutes they'll get back to their vibrant colors. Do guppies do this too? I usually watch my fish every morning, and never noticed my guppies do that before.
I'm going to put her in the breeding trap, just in case. I'm hoping it's not ammonia poisoning, but none of my other fishes have red tints to them. If she doesn't have babies by the time I get home, I may put her back in the main tank, so she doesn't get lonely.