Do black clothes really make you look slimmer?
The theory is that very dark clothes make your outline less visible in dim light; black makes you disappear against the background. Black is also held to better conceal creases and folds in your body. Regardless of whether invisibility is a desirable fashion goal, there is some truth to the disappearing-silhouette concept – television producers don't like their on-air guests to wear black because the dark studio background can make them look like ghostly floating heads.
But in daily life, where daylight generally prevails, there is no point to this or any other popular attempt at an optical illusion. Monochromatic dressing doesn't make you appear slimmer either, and wide collars don't make your face look wider. Black is popular because it suggests sobriety and seriousness (it is the colour of priests and mourning) and that in itself may make you appear, I suppose, slightly less like a sybarite.
It is true, however, that black can make the pale look even paler – something you may choose to cultivate, whatever frustrated TV producers tell you to wear.