Leaves are darker around edges?

[Smoky]

On one of the buckets the leaves are darker around the edges.
Is this normal or an indication of trouble.
Any help is defiantly appreciated.

[D.A.A.S.69]

Need to know more about your grow, like soil, coco, light, that kind of thing.
But if your new growth coming in at the top is green, I wouldn't worry to much, unless the whole plant starts showing bad leaves.