There is no single, definitive shade of rust. Rust is what happens when iron-based metal is exposed to oxygen over time, and it is generally a saturated shade of brown, red or orange. Rust is a sophisticated colour, often used in decorating schemes of libraries, dining rooms, bedrooms and dens.
Colours Found In Nature
Rust itself is found on iron metals and therefore might appear in any surroundings in combination with any colours. However, the colour of rust is a common colour in nature. Autumn leaves, certain types of iron-rich rocks, soil and sand, certain species of moths, and some trees all may have rust colours. A common convention when choosing a colour scheme is to choose colours that appear in combination in nature. To find the colours to match rust, choose colours that appear around it in nature.
Complementary colours are often seen as being "opposites." They appear across from each other on the colour wheel. Complementary colour pairs can also be the basis of a colour scheme. The complement of rust generally is a shade of green or blue--this will depend partially on the shade of rust, which is not a definitive constant. Digital imaging and illustration software can be used to find the complement of a colour, or you can simply check with a colour wheel.
Because rust is a warm colour, it fits well with other warm colours. Shades of orange, gold, red and warm browns often fit well with rust. Because of the variable nature of all of these colours, the exact combinations and exact shades that look right with the colour rust will depend on the particular shade of rust.