The Phal abuse ends here.

[Im Just Saying]

I'm not sure about yellowing along the edge of the underside of a leaf hopefully someone with more experience can help you with that. However in the case of the purplish edging if your blooms have red or purple coloring in them you will sometimes also see that along the edges of the leaves. I also believe that too much light can cause a purple tint to the leaves but I believe that is on the top of the leaf. I'm sure that someone more knowledgeable will correct me if I'm wrong though Hope that helps!