my plant is turning light green,real pale! what is wrong

i have a plant about 4 feet tall it was a nice deep green but in the past couple of weeks its getting light green. lime green now but i dont want it to turn yellow, help!

more info is needed, pics would help a lot but outside of that:

soil or hydro?
veg or flowering?
lights?
light distance?
nutes?
ph?

could be a mag. def. is it two shades of green on the same leaf? look into that

yea man its just started to happen with my beautiful MOB strains in the past week or so ( wierd!!) ive always grown in the same room and fed my girls fox farm nutes. iI cant figure out whays up but , will try to keep you fellow gardeners posted. Let me know too okay.

its in fox farm soil outside, veg state, using cns nutes, 6.5 ph