light green leaves

Hi guys and gals, this is my first grow soooo here goes. Not entirely sure on the strain, it was called purple durban. Not necessarily the most reliable source, but it probaby is what he said it was. It's a hybrid, 55% Sativa, 35% Indica. I have 9 plants going now. In early vegetative stage...

I have other plants in same soil, same nutes, that are dark green, this looks way too pale, any thoughts replied are urged!! thank you all!