I thought magnesium deficiencies began near the edge of the leaves? These plants just seem to have a little striping between veins. I am interested, because I have two plants that look a lot like this, but I haven't done anything, and they're coming along just fine. Personally I thought it was just a mild stress reaction to either transplanting or changing the color of the light.

For the time being, I'm doing nothing unless the plants start showing evidence of a real problem.