Purple Leaves - White Widow

Hey I have a white widow in organic soil under a 400w HPS and 7 Various Intensity CFL's. The plant is 27 days into flowering and I'm using fertilizer spikes to feed. The spikes are 6.0% occluded slow release nitrogen, 6.6% occluded slow release available phosphate and 8.4% occluded slow release soluble potash.

My problem is isolated to this plant and the leaves are beginning to turn purple. The veins in the main stem are as well.

Any ideas? I am thinking, because this is the tallest plant in the group, the roots may be bound in the soil, restricting the plant from absorbing the necessary nutrients. What are your thoughts?

low night temps is usually what causes purple and red leaves, nothing to worry about.

overnute is the cause of purple stems.

I got purple stems coming out of my 3 week old plants with no nutes added. I'm also having some purple leaves, which I was worried about, but it has been a lot cooler since they appeared, so I think pepsicola is right

ya purple stems are pretty normal for me

The color of the stems and leaves are also dependent on the genetic makeup of the plant in question. Some strains are predisposed to having purple leaves and stems when in the right environmental conditions (i.e. Indica strains in cooler weather, wetter/costal climates, etc.)
I'm unsure of WW genetic makeup containing purple phenotypes but another more experienced grower could probably help with that...or you could ask google...