Sorry you are feeling frustrated with the lack of responses.
Dawg is right it's probably the heat. He's pretty knowledable about chickens.
It could be drinking a lot of water, or it is normal for chickens to have cecal (watery dark) poo occasionally. If they are acting normal I wouldn't worry too much unless other symptoms show up or it continues for long. And by too long I mean they start in with other symptoms like refusing to eat, weak, or lethargic.
If you give yogurt the organic with probiotics are best. That's what will help the digestion. If they are not eating the yogurt, try mixing it into something they like.
You can feed them either cooked or uncooked rice, but I think Dawg was meaning cooked white rice, as it is easy to digest. And making it into a mash (rice pudding) type consistency
Colored poop can refer to a disease, but can also just be what they are eating. I'll attach a couple links.
http://www.welphatchery.com/poultry_health.asp
http://www.colchesterpoultryclub.com/health.htm
And ladrholman,
I hate the lethargic hen posts. Gets posted a lot and there never seems to be a good answer. Sounds like you are doing something for her. Without a diagnosis it is tough to recommend a specific anti-biotic. I wouldn't know which one anyhow. Is vet an option?
Good luck
Imp