The Node Appearance - Colors setting panel controls the background color and halo color for nodes. The Node Background is painted as a solid rounded rectangle and the Node Halo is painted as a translucent shape of the same color behind the node halo.
Node Type Colors
The colors in the Node Type Colors table indicate a "single" color for all nodes of that type.
The color displayed in this table will be used as long as the Node Color By table says "Single" in the Color By dropdown for this node type.
Clicking / Selecting a row in this table will change the selection in the Node Type combo box in the table to the right.
Node colors can later be changed using the Color Chooser dialog