Litmus paper is a common indicator used to determine the acidity or basicity of a solution. When litmus paper is dipped into dishwashing liquid, the presence of alkaline components in the dishwashing liquid will cause the litmus paper to turn red, indicating a basic solution. The alkaline nature of dishwashing liquids is due to the presence of ingredients like sodium hydroxide or potassium hydroxide, which are strong bases that react with acids to produce salts and water.