When the weather first turns warm, “Summer Hair” is the stuff of legend. Most of us imagine the sun doling out free highlights as the sea breeze teases our lobs into perfectly tousled perfection, certain we’ll resemble a Brazilian supermodel come summer’s end. In actuality, that is precisely when reality sets in — and we realize “Summer Hair” is, in fact, something totally different. Far from the benevolent gods you one imagined them to be, the sun and salt have instead left your hair a crunchy, brassy mess.