This system was based on designs evolved by John L. Baird.  In 1943, he designed a two color system, with two images produced on the face of a CRT. Lenses then converged the images.

Inside the viewing tube is a transparent screen having parallel ridges on the side toward the viewer and flat on the opposite side.  There are three electron guns whose beams are modulated by the three color band signals.  The beam from one of these guns can impinge on only one side of the ridges.  This side is coated with a phosphor emitting the color band which is to be reproduced by the corresponding gun.  The second gun can send its beam only to the opposite side of the ridges, this side being coated with phosphor emitting the second color band.  The beam from the third gun strikes the flat surface of the screen, which carries a phosphor emitting the third color band.  The third color, produced on the back of the screen, shows through the transparent supporting material and mixes with the other two color band produced on the sides of the ridges.  The ridges are very narrow and closely spaced. Two of the guns are in such positions that their beams travel different distances to opposite sides of the screen. (Information and pictures courtesy of Rick Plummer)

Here is some additional information, courtesy of Stu Andrews:

The system was called " Telechrome" and used modified theatre arc lamps as the basis for the three-gun CRT. Baird demonstrated the invention to several experts and newspapers at the time. The BBC publication "Radio Times" in 1942 described the picture as " entirely natural" . Several lines rates were tried, with the final versions of Telechrome running at 1000 lines. Baird died in 1946 and Telechrome was forgotten in the rush to re-start broadcast TV.

Popular Mechanics, March 1945

 

A photo of the Telechrome tube (Courtesy of the Science Museum/Science & Society Picture Library)