Different colours of eye shadow suit different eye colours. They highlight your eyes and add a splash of make-up colour to your face. The mix of colours gives structure to your make-up. A lighter colour can be applied to the whole lid. You can then add a darker eyeshadow tone to highlight the base of the lid.
Pretty much any colour of eye shadow goes with brown eyes, whereas blue eyes are better enhanced by apricot, mauve or grey shades. Lilac and plum flatter green eyes. Your eyes will be enhanced and highlighted in harmony with the colour of your iris.