Is there a way to set vertex color of selected vertices with single click? I have some objects that I want to set the vertex colors of.  While I can use my tablet to do this in vertex paint mode, for the project I'm working on, I just need to flood fill the selected vertices with my current color.  

Basically, I want to set all vertex colors to black, then pick a few faces and set the vertex colors of those to bright red.  Is there a faster way to do this, or do I have to hand paint all the colors?
You can apply the currently active vertex color for all vertices at once while in Vertex Paint Mode. Just select (Paint -> Set Vertex Colors) from the header menu. Basically, you set the dominant vertex color for the whole mesh and then manually paint a few vertices afterwards. 

While this doesn't work on a selection but only the whole mesh, you might want to split/join your objects beforehand. So that you don't need to paint too much geometry by hand. But there might be some alternative approaches to this like working with vertex groups or utilizing the vertex weight. But this might be the more straight-forward solution.