On 3-coloring of plane triangulations

Let G be a plane triangulation. For a 3-vertex-coloring λ, a face of G whose vertices receive all three colors is called a vivid face with respect to λ. Let hλ (G) be the number of vivid faces in G with respect to λ. Let C(G) be the set of 3-vertex-colorings of G and let g(n) be the set of plane triangulations with n faces. Let h(G) = max {hλ (G) ∣ λ ∈ C(G)} and h(n) = min {h(G) ∣ G ∈ g(n)}. s paper we show that h(n) ≥ 12 n for any even n, and that h(n) ≤ 15 (3n − 2) for infinitely many n.