pH indicators exist as liquid dyes and dye-infused paper strips. They are added to various solutions to determine the pH values of those solutions. Whereas the liquid form of pH indicators is usually added directly to solutions, the paper form is dipped into solutions and then removed for comparison against a color
Here is a chart of common pH indicators, their pH range, their solutions, and their color changes. Some indicators display multiple color changes, so they occur on the list more than once. Various references list slightly different pH values and colors.
INDICATOR PAPER with colour scale pH 5.5 – 8.0