''Phenolphthalein'' is another commonly used indicator, colorless in acid solutions and pink in alkaline solutions. Various other indicator dyes are known, which change color at various pH levels, and by mixing them it is possible to produce universal indicators that turn different, distinct colors at various pH levels. Universal indicator paper can be dipped in a solution, and the approximate pH read off by matching the color against a printed color scale. | ''Phenolphthalein'' is another commonly used indicator, colorless in acid solutions and pink in alkaline solutions. Various other indicator dyes are known, which change color at various pH levels, and by mixing them it is possible to produce universal indicators that turn different, distinct colors at various pH levels. Universal indicator paper can be dipped in a solution, and the approximate pH read off by matching the color against a printed color scale. |