Leaf discoloration?

[ClosetGrower2]

My seedling is showing a light yellowing of leaves and I have some dark spot on one leaf. What could this be?

 

[PiztilsPlease]

Overwatered/underwatered wait till the first two inches are bone dry before water and put lots of drainage holes in the bottom

 

[thinkbetter12]

It needs a bigger pot than a solo cut by the look of the size.