I created an addon for transfering selected weight to a vertex color group. You can copy the values either as grayscale or color(as shown in weight mode).
I created this addon mostly for rendering purposes however I am sure there are other uses. Basically sometimes it is easier to create masks by selecting some components in edit mode and creating a weight group from the selection. Once done you convert that into vertex colors to use as masks or colors for rendering.
You need to make sure that you at least have one weight and one vertex color group selected. Once done just fire “Weight2VertexCol” command.
Please let me know if you see any bugs, or have feature requests. I have not tested it heavily as of now.
Btw the monkey in the screenshots is a model I have given away free sometime ago. You can download the free blend file from some places on the net. I do not have a direct link though.