Hi, Well it sounds like your egg cartons are beginning to grow some moss or disintegrate. That's why I always use plastic growing cells or pots to start my seeds. I don't think the green on the egg cartons will cause you any problems, but it is a sign you may be overwatering. Be sure those egg carton cells have a drain hole in the bottom of each one so excess water drains away. If your soil stays too wet, those seeds won't germinate.