It's actually not uncommon in very young plants and since you don't even have true fan leaves going yet, it's nothing to worry about. Young leaves can exhibit all kinds of weird colorings, can be misshapen etc... Relax, take a deep breath and wait until you have some fan leaves going to assess whether or not there's an issue. At this stage of the game, you wouldn't want to start adding nutes anyway... just make sure you're watering with ph'd water and you'll be fine.