Final answer:
Replacing red light with blue light in a single slit experiment makes the diffraction pattern narrower with closer-spaced fringes, due to blue light's shorter wavelength.
Step-by-step explanation:
In a single slit experiment, when red color light is replaced by blue color light, the diffraction pattern becomes narrower and more closely spaced. This is due to the fact that blue light has a shorter wavelength than red light, and the pattern of diffraction is directly related to the wavelength of the light used. Since the blue light has a shorter wavelength, it will diffract less than red light, resulting in a pattern with smaller spacing between the fringes.