Colorful heels are fashion accessories that have a way of taking a simple outfit and making it seem far more dressed up. The key is not making the colorful heels compete against the rest of the outfit for attention. Most people look best when wearing colorful heels with simple outfits, like jeans, as well as skirts and dresses in classic colors (the way Carey Mulligan does, in her cobalt heels with her black and white outfit). It’s a fashion style that may be on its way to becoming a classic.
You don’t want to mix colorful heels with a colorful outfit, unless you want to look like a Disney extra. In general, the brighter or more unusually the heels are colored, the more neutral or classic the rest of the outfit should be. Jeans, classic suits, the little black dress: all are good candidates for pairing with colorful heels. Also, if your colorful heels feature any sort of pattern (zebra, leopard, etc.), keep the rest of the outfit in solids so you don’t overwhelm the eye of your beholders.