You have probably seen a rainbow, or light separating into colors through a cut-glass window.
You can make your own color spectrum reflect on a wall or ceiling this way.
Lean a mirror against the far end of a shallow pan filled with water, the whole mirror does not have to be underwater.
Position the pan so that sunlight, or bright starlight, hits the submerged mirror. Adjust the mirror until you throw a “rainbow” of color against a nearby surface, for example, a wall or ceiling.
You will see the clear light become violet, blue, green, yellow, orange, and red, in that order.
