[Math] How many ways can we color a regular tetrahedron with two colors

Question

A regular tetrahedron is a polyhedron with four faces that are congruent equilateral triangles.
How many ways can we color it with two colors? Two colorations are the same
if we can rotate a colored tetrahedron in one way, so that it looks like the second coloration. The two colors do not necessarily have to be used.

Answer 1

Color patterns in cases where certain colorings are considered equal are counted by the so-called Polya Theory, AKA "Burnside Lemma". But we don't need this theory in the simple example at hand.

The two colors can be partitioned on the four faces of the tetrahedron in a $0+4$, $1+3$, or $2+2$ way. The $0+4$ and $1+3$ types can be realized in two ways each: $0$ red and $4$ blue, or $4$ red and $0$ blue; similarly for $1+3$. For the $2+2$ type its different: If you paint two triangles red these two triangles share an edge, and the two remaining triangles, to be painted blue, share the opposite edge. It follows that there is only one color pattern for $2+2$.