What's the use of apply color?
 

I would like to know what's the use of Edit Polygons > Colors > Apply Color. The color is instantly applied while modeling but I it doesn't appear to do anything in the render stage. I suspect there must be a shading utility which let's one use the vertex color data and connect it to the object's color, for instance, but couldn't find which one or even if I'm right.

Now Im not %100 sure on this, but my guess is that its used when modeling to tell diferent objects apart from each other. But then agian, I could be wrong.

yes. I agree.
 

I agree with him.