Black is universally recognised as being the one colour which can help you look a few pounds lighter, although even the largest of people will never look thin in black: it can only help a little. Any dark colour such as navy or dark brown will also help a little.
Black generally makes things look smaller, so if you have large hips, then black will help make them look slimmer. White and yellow can often accentuate size and make someone look a few pounds heavier than they are.
Horizontal stripes make you look wider and draw people's attention to the width of your body, so they should be avoided by anyone who is overweight.
Vertical stripes can help you look slimmer, since they draw the eye to a person's height and the length of the body, so they can also help make you look slimmer, particularly if the stripes are black or navy.
Black generally makes things look smaller, so if you have large hips, then black will help make them look slimmer. White and yellow can often accentuate size and make someone look a few pounds heavier than they are.
Horizontal stripes make you look wider and draw people's attention to the width of your body, so they should be avoided by anyone who is overweight.
Vertical stripes can help you look slimmer, since they draw the eye to a person's height and the length of the body, so they can also help make you look slimmer, particularly if the stripes are black or navy.