strict graph {
  overlap="false";
  node [shape="circle", label="", style="filled"];

  1 [fillcolor=blue];
  2 [fillcolor=red];
  3 [fillcolor=green];
  4 [fillcolor=yellow];
  1 -- 2;
  1 -- 3;
  1 -- 4;
  2 -- 3;
  2 -- 4;
  3 -- 4;
}
