Chromium is used to make boat propellers. It also was used as the magnetic compound in cassette tapes. The chromium compound chromate ( CrO42- ) is yellow, while the chromium compound dichromate (Cr2O72- ) is orange. Compounds that contain transition metals (like chromium) are often brightly colored, and they can display multiple colors. The presence of chromium in rubies imparts the red color to this precious stone.