Total internal reflection is taught in school science labs using a semi-circular glass block. A ray box shines a light ray onto the glass. The semi-circular shape ensures that a ray pointing towards the center of the flat face will hit the surface at right angles.This prevents refraction at the air/glass boundary.
At the glass/air boundary what happens will depend on the angle.
|θ1 <θc||θ2 >θc|
| the ray will split.
Some of the ray will reflect off the boundary,
and some will refract as it passes through.
|All of the ray reflects from the boundary.|
None passes through.
The colour of the rays in the diagram is there to easily distinguish the rays, it is not meant to indicate any colour dependence.
This physical property makes optical fiber useful and the rainbow in the sky and binoculars possible.