Die Anzahl der Faerbungen ebener Graphen
  Let G be a finite planar connected graph without loops or multiple edges. All minimal circuits except atmost one - say C* - are triangles. Let k be the number of vertices of C*. There are at least 2**(k-3) colorings of the vertices of G with four colors, vertices connected by edges colored differently. These colorings are different on C*. 
L. Friess