Litmus is a water-soluble mixture of different dyes extracted from lichens. It is commonly used as an indicator in chemistry to test whether a solution is acidic or basic. Litmus turns red in acidic solutions and blue in basic solutions. The change in color is due to the protonation and deprotonation of the litmus molecule. In acidic solutions, the litmus molecule gains a proton (H+) and becomes positively charged. This causes the molecule to absorb blue light and reflect red light, giving the solution a red color. In basic solutions, the litmus molecule loses a proton (H+) and becomes negatively charged. This causes the molecule to absorb red light and reflect blue light, giving the solution a blue color.