If the bird just had the tips turning purple but was otherwise acting OK, I would say dehydration as I have seen this before.
Purple and black indicate a lack of oxygen and blood flow to an area.
runny, green poo can be caused by a bird who is only ingesting water or not ingesting anything at all and it can be a sign of dehydration. Combs can turn purple from pneumonia but it's generally a all over maroon color with that. The ends turning purple or black and it gradually going lower...
I am very sorry you are going through this but this is usually a sign of hearth failure. It is nothing you did or have done and is a problem that seems to plague roosters more than hens. In all my experience with this (I've lost 2 from it) the best thing to do is keep them comfortable until...