Yellowish, purplish/brown on leaves

So I started my plants from seeds. They are just now developing there top leaves... still only about 3 - 3 1/2 inches tall, still babys. This is my first time. Although I have helped friends. One of my babys was looking like its leaves where going to develope purple on the edges, but this morning when I went to check it looked more purple/brownish and some of the leave had fell off completely. probably a 1/4 of it. Not all the plants have yellowish leaves, but probably 4 of 6. Two look great and really green and healthy. I know the first leaves are suppose to turn yellow and fall off, most of them are starting to turn yellow, but also some of the other leaves, what could this be... not all my plants are having it, any advice?

could it be from water getting on the plants? I was spraying the soil with a spray bottle to get the humidity up, im guessing a hit a couple of the plants with some water... would it be burnt?