Ultraviolet–visible spectroscopy uses visible and ultraviolet light to look at how much of a chemical is in a liquid. The colour of the solution is the basis for how UV-Vis works. The color of the solution we are working with is colored because of its chemical composition. So the solution absorbs some light colors and reflects other colors, the light it reflects is the color of the solution. UV-Vis spectroscopy works by passing light through a sample of your solution then determining how much light gets absorbed by the solution.