title: Colored graph isomorphisms: 1(red)->2(blue) vs 1(blue)->2(red)
body: <p>Given two simple graphs:</p>
  
  <pre><code>library(igraph)
  
  g &lt;- graph.empty()
  g &lt;- g + vertices(1,2,3)
  g &lt;- g + path(1,2,3)
  
  
  g1 &lt;- g
  V(g1)$color = c(1,2,2)
  g2 &lt;- g
  V(g2)$color = c(2,1,1)
  </code></pre>
  
  <p>which look like:</p>
  
  <pre><code>par(mfrow=c(1,2))
  palette(rainbow(3))
  plot(g1)
  plot(g2)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/5DdxP.png" alt="graphs"></p>
  
  <p>How come they are not isomorphic?</p>
  
  <pre><code>graph.isomorphic.vf2(g1,g2)$iso
  </code></pre>
  
  <blockquote>
    <p>FALSE</p>
  </blockquote>
  
  <p>and most important, if this is not an isomorphism, how can I detect this kind of equivalence within <code>igraph</code> ?</p>