They are heavy feeders...... if you'd been following along, you would have known that already. I'm up around 1000 ppm right now under the LED's, although tonight's feeding I dropped to 850 ppm. Last time I grew it under HPS, I was up around 1200 ppm for most of the grow. They like a lot of Cal/Mag too, as I'm up around 8ml per gallon on average these days.
While thinking about this, I think the lighter coloring on the plants is caused by all the white light from the LED's. I've really tried to green them up some more, and they were slow to budge. Now, when I go in with a regular flashlight, most of the plants are nicely green (not light green).