Titan yellow is a compound with formula C<sub>28</sub>H<sub>19</sub>N<sub>5</sub>Na<sub>2</sub>O<sub>6</sub>S<sub>4</sub>. It is a triazene dye used as a stain and fluorescent indicator in microscopy. It is also used for the colorimetric indication of various compounds and is an acid-base indicator. As an acid-base indicator, it changes color from yellow to red between pH 12 and pH 13.