Adjusting Thickness
Line thickness is a global parameter that applies to all curves, whether imported as DWG/DXF in Fast Rendering or Editing mode, or drawn directly in NUBIGON. You can adjust this setting under Edit > Preferences > CAD.
Adjusting Color
Curves - Fast Rendering Mode
DWG/DXF curves imported with the default Fast rendering option are displayed with this icon 
in the Object List. To adjust their color, click on the color box and select the desired color.
Curves & Points - Editing Mode
Curves and points imported with the Editing option, or drawn directly in NUBIGON, inherit the color of their parent group object. Changing the parent group's color automatically updates the color of all curves under that group.
To change the color of a group object
, click its color box in the Object List and select the desired color. 
Ungrouped curves are displayed with the Line color set in Edit > Preferences > CAD, and ungrouped points are colored by the Point color. A newly generated group object will inherit the Layer color.