Apply effect to only part of the mesh

Hey guys! I'm going to try to explain this as clearly yet shortly as possible, however please forgive me if it is not clear as it is a small part of a huge project.

I have a mesh that is generated from many smaller meshes, in this case hexagons, akin to a chucking system. Textures are read from a texture atlas. My question is what would be the best and most efficient method to make a change to one hexagon without adding an extra element to the texture atlas? For example, to gray one hexagon out without having to add a grayed out texture for each hexagon texture to the atlas?

A vertex shader?

While code is always welcome, simply a push in the right direction would be tremendous help.

Best regards,
Landon Kirk.

 

Vertex colors? 50% alpha would probably work.

--Eric

 

I'm not rehearsed in these areas very well. Is this the same as vertex lighting?

 

Nope, it's Mesh.colors32. Each vertex has an associated color. That requires a shader that makes use of vertex colors; most of the built-in shaders don't, although the particle shaders and sprite/ui shaders do.

--Eric