title: Can we 3-color a graph in polynomial time if we know the graph is 3-colorable?
body: <p>I understand that to decide if a graph is 3-colorable is NP hard. But I was wondering that, when we are given a guaranteed 3-colorable graph, can we 3-color the graph in polynomial time? 
  Most of the resource I found are talking about deciding if a graph is 3-colorable... I am not sure what keywords I should put in google to get a better search result... So I am here. Any help would be greatly appreciated.</p>