We have all heard the rumour black makes us look slimmer and white makes us look heavier. But there are other ways to create similar effects without limiting your wardrobe to black or white.
Any dark colour will have a slimming affect. So why limit yourself to black? Clothing in lighter colours has the opposite affect. Light colours reflect light which causes an area to appear larger.
Clothing in muted colours has a similar effect to black. Because they absorb light they will have a slimming affect. Bright colours like white reflect light and will make an area appear larger. This will have a similar effect in clothing.
Clothing from the cool side of the colour wheel also has a receding or slimming effect. If cool colours suit your colouring you have an advantage if you want to look slimmer. Warm coloured clothing will make the area appear bigger.