title: Minimum vertex coloring
body: <p>I'm looking to find the best solution for different instances of graphs (which ranges between 3000 edges to 70,000) in which I should color the vertexes in minimum colors.
  Two connected vertexes must not be in the same color.
  I used a greedy algorithm which gave me perlimenery results and I managed to improve it by giving colors first to the highest ranked vertex, but it's still not enough.
  Wanted to ask if there's any known libraries in python for coloring graphs or any algorithms that might help improve my colorings even more.</p>