Color Difference.

I have the exact same thing at the moment - 2 x northern light auto - one is a big fat indica looking girl and the other isnt

Every strain has different phenotypes that each have their own characteristics & requirements

No two plants, even of the same strain, will have identical requirements. The pale plant obviously has a hungrier appetite. Just like people, you could have the same parents, but your brother/sister might like oysters but you yourself hate them, so it is with plants, what may be enough food for one plant, might leave the other one with an empty stomach. Giving the pale plant a bit of extra nitrogen and it should green up soon enough. Hope this helps, Organoman.

Different phenotypes. You could plant 10 seeds all of the same and from same breeder. You will see they all grow slightly differently with different traits. You might get a few that grow similar and look similar out of the 10.

Happens all the time. Two different phenos. They can look completely different, smell different, and feed different. Based on the pics, they both look healthy. Good luck! ✌️🏻💚🌿💨

Yes they are both health but when it come to the same strain and they leaf color then it can mean anything from the breeders like if you got the same strain but by two different breeder that can happen or can go off of many things but so far doing some Searching you look good but do research yourself great grow I must say.

Different phenotypes.