vertex painting RGB logic

Hi, I tried vertex painting and it is not as simple as I thought to be. I was thinking that the RGB channels each is a material selection that I can pick to paint onto but it’s not that straight forward.

When I select the R channel or the G channel, it doesn’t paint anything unless I switch the black/white color or using the shift erase key. And when I view using RGB channel, the model turns blank or empty. I don’t quite understand why there is no color information.

Anyone can explain the logic behind vertex painting RGB?