[Boost-users] [Graph] source vertex colour at start of BFS or DFS

Hi, I'm wondering, why do the BFS and DFS algorithms not inspect the colour of the source vertices given to them? If a source vertex is already black, shouldn't the search effectively be a no-op? Currently the source vertex is 'discovered' and coloured grey regardless of its previous colour. I know it might seem weird to pass a black vertex as the source, but I guess I see it as similar to passing an empty range to an algorithm: it's valid but nothing happens. Thanks, cheers. Jeremy