Leaf Turning Black in Chili Pepper Plant
There is one leaf that has turned a light purple/black and there are two others that are starting to do the same, at the top of the plant. The plant looks good otherwise. There are six other plants around it that show no sign of leaf color change. The plants were transplanted three weeks ago in good improved soil.
If it's only 2 or 3 leaves, I wouldn't be too concerned. If the plant has 25% or more affected leaves, I would take a sample to my local agricultural extension office for identification and recommendations.