Vertex colors will be set depending on the selection mode.
Vertex, edge and face select modes (
TAB) each have different effects.
Vertex Color Layers:
Select the currently active vertex color layer. Add and remove layers with the + and - buttons.
An easy to access color selector to select the color hue and shade.
The Set Color button sets the color to the selected vertices/edges/faces.
The Get Color button gets the color from the selected vertices/edges/faces.
Click on the color preview button to get a more detailed color wheel that supports RBG, HSV and Hex values and a color picker.
These buttons can be used for easily shading a mesh. They range from black to white.