DISCOLOURED is a term used to describe something that has changed colour, usually due to age or exposure to the elements. LIVID is an adjective meaning very angry or enraged, and RUSTY is an adjective meaning covered in rust, which is a reddish-brown oxide coating that forms on iron or steel when exposed to air and moisture. Therefore, DISCOLOURED can be described as something that has become LIVID or RUSTY due to age or exposure to the elements.