The plot thickens....
It needn't.
Various palettes exist in a most arcane location.
Tools/Color Palettes, select the down arrow just left of "Save as" all of the palettes located in your Support Files folder should appear including Default. Unless you have changed your default colors as suggested above, it should be the original. Or just copy the original from a previous version of DataCAD.
.rgb files must exist in the Support Files folder in DataCAD 11 & 12. In DataCAD 10 and previous, one could load from any folder. An .rgb file is a text file that can be examined in Notepad.
in furtherance: from the DataCAD Revision History:
05. The Tools, Generate TBL File menu has been renamed to DXF/DWG Color Map. When selected, a color mapping table (.TBL) corresponding to the active color palette (.RGB) is either generated on-the-fly if one doesn't already exist, or is automatically loaded if one already exists.
The Update, Create, and Close options have been replaced with two options, OK and Cancel. OK saves any changes that have been made and closes the dialog, and Cancel discards any changes that have been made. If the Translate colors using color mapping table option is active during DXF/DWG export and a corresponding .TBL file does not exist, DataCAD will automatically map DataCAD's colors to the nearest color in the DXF/DWG palette.
It seems the default (dxf/dwg) table is built-in, to use a different table, copy your older file.