Red rust is a result of exposure to elements such as air and water. Unlike other rusts there are no visible rust runs or streaks as the affected area is usually affected as a whole by atmospheric conditions. Like black rust, this form of corrosion is formed when combined with salt.
Yellow rust usually appears in places of high moisture content where the affected area has been highly exposed to water over a period of time and has corroded as a result. The yellow rust stain usually appears to run or drip.
Unlike yellow rust, brown rust is a drier and crustier rust, formed as a result from contact with water and oxygen. It is similar to red rust, however, brown rust appears in patches rather than affecting an entire surface.
Black rust usually forms in a low oxygen environment. The black stains help to indicate where the issues are. For the example areas where the rust is, indicate a lack of oxygen. Black rust, like red rust can form as a result of contact with salt which causes corrosion.