ha yeah man i've been there too... this stage of the growth is the most intensely stress for the grower, you're always stressed hoping to get a good result. Good news is there's nothing to worry about - the leaves are in full expansion so sometimes they're gonna get a bit darker a bit lighter or even a bit purple in your case. Nothing to worry about so chill, and enjoy the show. At this early stage you can even see the plant growing hour by hour, it's amazing. Good luck my friend - i'm rooting for you !