AutoCAD Color Index (ACI)

The color attribute represents an ACI (AutoCAD Color Index). AutoCAD and many other CAD application provides a default color table, but pen table would be the more correct term. Each ACI entry defines the color value, the line weight and some other attributes to use for the pen. This pen table can be edited by the user or loaded from an CTB or STB file. Ezdxf provides functions to create (new()) or modify (ezdxf.acadctb.load()) plot styles files.

DXF R12 and prior do not preserve the layout of a drawing very well, because of the lack of a standard color table and missing DXF structures to define these color tables in the DXF file. If a CAD user redefines an ACI color entry in a CAD application and does not provide this CTB or STB file, you can not know what color or lineweight was used intentionally. This got better in later DXF versions by supporting additional DXF attributes like lineweight and true_color which can define these attributes by distinct values.