Question

which colour of light has a light critical angle red light or green light

Answer 1

The critical angle depends on the index of refraction. The index of refraction can depend on the wavelength (color) of the light; this phenomenon is called dispersion.

So yes, in a material with dispersion, the critical angle can depend on color.

Answer 2

Green light has a smaller critical angle than red light because the refractive index of green light is greater than the refractive index of red. As the refractive index increases, the critical angle decreases..

Hope you understand