I would keep an eye on a chick with any red in their poo. It may have been just something they ate, and may pass on its own, but it could indicate a problem.
Check the chicks vent. Are there any wounds that you can see? Is the chick prolapsed (part of the inards protruding from the vent...like a hemroid)? Is there alot of poo stuck to their bottom (pasty bottom)? If you notice any of this you'll need to fix it right away before it gets worse, or the other chicks start pecking at its bottom. The chick could then get shocky, stressed, or bleed to death. Blood in the poo (if it is blood your seeing) can also be a symptom of Cocci in chicks.
If you dont see any of the above, I would just seperate the chick for a day or so and see if it has anymore "red" in the poo. If not, then I would assume its fine to put back with the others.
