Plants need sunlight to make chlorophyl. Given a few days in the sun, they'll green right up. That being said, there is a great deal of energy stored up in the root system, so being covered for a short amount of time won't do them any serious harm. However, I would amend my previous statement to suggest adding a thin layer of compost (~1") for now. You don't want to make their job of finding the sun any harder, but you do want to feed and protect them. Then add some more in a few weeks when they've grown a bit.