Leaf color

Quick question, I've got a little bagseed growing in my closet. there is one thing im wondering about. ive noticed that the leaves are darker in color in the middle and lighter green (not yellow) towards the outside.

what causes this and is this bad?

because the outside leaves are recieving more light then the ones in the middle i dont think its bad but this is my first grow so seek more advice from the more experince people on here. Good luck with the grow tho man!

Im talking the individual leaves themselves. They are darker near the veins and lighter towards the edges.