I'm guessing they got sunburned. You can't just put plants out into direct sun if they're not used to it. You have to acclimate them by putting them in only 1 or 2 hours of sun at first, then gradually increase over about a week. Either that or make sure you plant them in only partial sun.

You should not have put them outside yet if you are getting 12 hours of light. That is unless you just want them to start flowering now. I like mine to veg 1 or 2 months before budding, so I get some weed for my efforts. I wonder what's going to happen when they flower, then in a few weeks the days get longer and they start vegging again. Weed is a short day plant, which means it will start budding if it gets less than 14 hours of light or so, depending on variety.