darkening

Someone should be able to recognize this, and it happens on a repetitive base, with different strains. Right around week 4-5, there is a sudden darkening of the canopy that happens literally overnight. One day they are all light green and lime and the next they get dark and remain that way...

First grow- are these tiny white spots something to worry about!? Am I over analyzing? I feel like an over protective mom or something....! What about the darkening in the middle? Any advice or knowledge is appreciated!