Red, orange, yellow, green, indigo and purple will appear white when they are focused at one point, because sunlight is the combined light of seven kinds of light.

Light with different frequencies is composite light. In fact, most of the light we can see is composite light. Sunlight, incandescent lamps and fluorescent lamps are all synthetic light, only laser or synchrotron radiation, or atomic spectrum. It's monochromatic light. Firelight is also synthetic light. All the combined light will be scattered when it passes through the prism.