Science, Tech, Math › Science Universal Indicator Share Flipboard Email Print GUSTOIMAGES/Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry in Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate by Anne Marie Helmenstine, Ph.D. Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. Updated February 22, 2019 A universal indicator is a blend of pH indicator solutions designed to identify pH of a solution over a wide range of values. There are several different formulas for universal indicators, but most are based on a patented formula developed in 1933 by Yamada. A common mixture includes thymol blue, methyl red, bromothymol blue, and phenolphthalein. How Colors Are Used Color change is used to identify pH values. The most common universal indicator colors are: Red 0 ≥ pH ≥ 3Yellow 3 ≥ pH ≥ 6Green pH = 7Blue 8 ≥ pH ≥ 11Purple 11 ≥ pH ≥ 14 However, the colors are specific to the formulation. A commercial preparation comes with a color chart that explains the expected colors and pH ranges. While a universal indicator solution may be used to test any sample, it works best on a clear solution because it's easier to see and interpret the color change. Continue Reading