Graph[{{{1, 3}}, {{2, 3}}}, 
 {{{-1., -1.}, VertexColor -> RGBColor[0., 1., 0.]}, 
  {{1., -1.}, VertexColor -> RGBColor[0., 1., 0.]}, 
  {{0., 0.}, VertexColor -> RGBColor[0., 1., 0.]}}]
