The business about white before Easter and after Labor Day isn't an old wives' tale; it was a fashion rule. You could ignore it, but to do so would have marked you as a clueless frump. Many younger women find it hard to understand now, but up until the mid-1960s, there was an accepted set of such fashion rules that delineated the tasteful from the tasteless, and no one wanted to be on the wrong side of that divide. It extended to hem lengths; Women's Wear Daily would decide what the "right" skirt length that year would be, and nearly every woman in America under age 70 and over age 12 would scramble to re-hem every skirt and dress she owned to the "correct" length. Other such "taste" rules included a rule that no clothing with sparkly trim could be worn before 5 pm, and the rule that your shoes must never be lighter in color than the lower half of your outfit. You always wore a girdle when going out in public (even very thin women did, to prevent the possibility of jiggle of any kind), and always, always wore a slip with an unlined skirt or dress. Also, it was NEVER acceptable for any part of your underclothing (such as a bra or slip strap) to show beneath your outer clothing.
Now then, here's my old wives' tale contribution: going outside with your hair wet is an immediate and inescapable cause of death. (Though somehow it didn't necessarily apply if you got caught in the rain and your hair got wet AFTER you were already outside. No one ever seemed to be able to explain that part.)