Yes to all the previous comments. And I don't think you seedlings are turning yellow, they haven't turned green yet. Notice that the yellow ones haven't been up as long. With adequate light, seedlings are green directly out of the ground, but if light is lacking, it will take more time to develop green (or they will stay yellow).
Removing the plastic completely all at once can be drastic. Here's what I would do: First slit the plastic lengthwise the whole length to decrease humidity, and move the light twice as close. Would that make it 1 ft away? it's hard to know for your pics. Leave it this way for a few days. You will probably find that growth will stifle as the seedlings adapt to new, better environment. As long as the seedlings still look good, you will be able to increase the light and open the plastic more and more, until you completely remove it.
