File with a .CTB extension contains information on colour styles of a two-dimension printout or mapping of colours on the layers of 3D objects designed in CAD 2D and 3D software. It is an old format, which is currently being substituted by STB files, which operate in the object layer of the abstraction.

These files are used in AutoCAD projects to configure colour schemes and object display properties. They cannot be used in a single project simultaneously, however, utilising AutoCAD, they can be converted from CTB into STB format.