Different colors of light have different wavelengths, so they will interfere slightly differently. Using one color lets you see the interference clearly."Every color produces its own pattern, with a spacing between the maxima that is characteristic of the wavelength. With several colors, the patterns are superimposed and it can be difficult to pick out a single maximum. Using monochromatic light can eliminate this problem."
The double-slit experiment, sometimes called Young's experiment (after Young's interference experiment), is a demonstration that matter and energy can display characteristics of both waves and particles, and demonstrates the fundamentally probabilistic nature of quantum mechanical phenomena.
