yellow plant!

hey, I have two plants of the same strain growing side by side in my vegtable garden. right beside the green peppers I treat the plants exatly the same. I water them the same amount I fertalize them the same amount everything is identical. But one of them is almost completly YELLOW while the other is completly green!! what could be the cause???

it could be a lot. could be nute lock. how old is the plant? flowering? pic give more info plz

the plant is a bit over a month old, its not flowering yet but i think i can see some preflowers coming up

in the process of uploading some pics

sounds like nute lock to me but im not quite sure what else it could be. it could be an mg deficiency but if it is from what you explained it would be bad

here are the pics

thats from not enuff or to much nitrogen isnt it ?

looks like a nitrogen or zinc deficiency to me, but i'm no expert