I learned its power in high school. By college, I was more likely to wear all white with a smidgen of black (perhaps the shoe)--a touch of malice :-) . Today I wear all black about twice a month. Never fails to make me feel strong and professional.
Still can't purchase H&M online, but at least now you can look more closely online at each item they sell. Dress above comes in four colors, and I think it might also work as a tunic. Will check it out this weekend and let you know.