Connect the respective Vertex Color tag whose data should be read or set here.
Internally, all object vertices are numbered consecutively (beginning with 0). This index number can be used to read or set the color or alpha value of the respective vertex. In the image above, for example, the first vertex was assigned a random color using the Constant node.
An alpha value (Type Real, 0=black, 1=white, grayscale for in-between values) can be fed into this input port.
Any color can be fed into this node that will be used to color a vertex.
This output port contains the color of the vertex defined by the Index port.
This port defines the alpha value of the point defined by the Index node.
The point count for the tag assigned to the object is displayed here.