Ok descriptions are nearly useless because your idea of "yellowish" or "green ones" is not the same as everyone else's. Upload a photo and people will be able to really diagnose the problem. Unless you have too much heat and are burning it like that, it sounds like a deficiency but the reason why can be many things like PH, root health, not enough nutrients, too much of some nutrients blocking others, salt build up... it goes on. Just make sure you know about all those things and try to get it all right.
As for root space, it's really important for lots of reasons to not let the roots get cramped- let alone binding up in a dense ball. Let's just say who cares what it does- just don't let it happen!. I mean c'mon, what will happen if you shoot yourself in the eye with a paintball gun? Partial or total blindness? Answer- don't do it!
If your roots don't have room to expand without bunching up, re-pot now. After a few grows you should know the appropriate size pot by looking how tight it all is when you're done and pulling the plant out.
think of it that way..
