A color value made of red, green, blue and alpha, each between 0 and 1. Values outside that range are clamped.
Amount of red, 0 to 1.
Amount of green, 0 to 1.
Amount of blue, 0 to 1.
Opacity: 0 is fully transparent, 1 fully opaque.
Values the block gives besides its output. The editor lists them under Properties, and an input can read one by reference.