Relation between critical angle and refractive index of medium is given by sinθc=1n
where, θc is the critical angle and n is the refractive index of medium.
Since refractive index of medium is lesser for red light as compared to green light i.e. nRed<nGreen
⟹ sinθcRed>sinθcGreen
⟹ θcRed>θcGreen
Thus red light has higher critical angle than red light.