I asked this on StackExchange TCS but did not get a satisfactory answer:
Four Color Theorem is equivalent to "Every cubic planar bridgeless graphs is 3-edge colorable". However, 3-edge coloring of cubic graphs is $NP$-complete. I'm wondering if the problem is still hard for cubic planar graphs.
What is the complexity of 3-edge coloring for cubic planar graphs?
Also, It is conjectured that $\Delta$-edge coloring is $NP$-hard for planar graphs with maximum degree $\Delta \in${4,5}.
Has any progress been made towards resolving this conjecture?
Marek Chrobak and Takao Nishizeki. Improved edge-coloring algorithms for planar graphs. Journal of Algorithms, 11:102-116, 1990
