OH Man, I agree with you. There are a lot of misleading pics on the net. (if it;s on the internet.. It must be true!) lol
One thing that I found out a later date was that a flash will show different colors on a fish at times. So it's best to take a photo with lights on in the tank, at night and with a slow shutter speed. although you may not the most crisp photo ever, you'll still get a more accurate depection of the fishes actualy visible color.
The only thing that I've ever felt okay with doing to a photo was increasing the brightness of it and cropping it. Sometimes theres just not enough light in the photo for some reason but it's still a good photo. But that's on a rare occassion anyhow as I've learned to not take photos of fish that at the end of the tank. I use shorter lights than the tank on most of my tanks. Center of the tank has the most light.