To create/export to a STL file click the Tools→Export→ button.
A STL file contains a description of the PCB in 3D and is suitable for 3D printing.
STL (Stereo Lithography) is a file format native to the stereo lithography CAD software created by 3D Systems. STL is also known as Standard Tessellation Language. This file format is supported by many other software packages; it is widely used for rapid prototyping and computer-aided manufacturing. STL files describe only the surface geometry of a three dimensional object without any representation of color, texture or other common CAD model attributes. The STL format specifies both ASCII and binary representations. Binary files are more common, since they are more compact.
An STL file describes a raw unstructured triangulated surface by the unit normal and vertices (ordered by the right-hand rule) of the triangles using a three-dimensional Cartesian coordinate system. STL coordinates must be positive numbers, there is no scale information, and the units are arbitrary
The Save to STL dialog is shown below.
Save to STL Dialog
STL files have no color.