Steve,
I guess the answer to CBS using their own in house equipment for prewar color demos would be CBS's head of research Peter Goldmark. Goldmark and his CBS engineering staff designed and built the color equipment at a time when television broadcasting was just in it's infancy. William Paley, head of CBS, thought he could jump start tv with an early introduction of color. CBS did purchase and use RCA iconoscope b&w cameras for their pre-war tv broadcasts. CBS also used RCA b&w tv gear during the postwar years. CBS, I believe, continued to employ their prewar color equipment for a short time after the war. The sequence of CBS color in this period is well documented on Ed Reitan's site: Early Color Television Studio Facilities
http://www.novia.net/~ereitan/studios.html
Including the FCC approved 1951 field sequential broadcasts. After this failed attempt at color broadcasting, CBS continued in 1953 with a modified RCA TK-30 field sequential to NTSC hybrid, called Chromecoder, to produce an NTSC compatible color picture. When this proved impractical, CBS reluctantly purchased in 1954, an all electronic RCA TK-40 color camera. Shortly thereafter the Chromacoder system was discontinued and additional RCA color cameras were purchased. A bitter pill for Willam Paley to swallow. I don't believe DuMont ever offered a true broadcast color camera (search: "Vitascan") and GE's color equipment may have trailed RCA both in availabiity and quality. Comments and corrections certainly welcome.
-Steve D.