Vertex colour shader with emissive multiplier

Hi

I am trying find a shader or get one written that does the following:

Uses vertex colours to provide both diffuse and a bit of emissive colour. This is for a mobile game. I think what I need to do is add half of the vetex colour values to an emissive component of a shader so that I can brighten it up a bit. Also I need a texture slot to multiply the whole colour component by to add details.

I was wondering whether it was possible to use a black and white texture to add details.

Imagine the following:

1. Mid grey has no effect on the colour.

2. Darker greys darken the colour.

3. Lighter greys add white to the colour.

Thank you

Jezza