My, admittedly brief, delving still leaves me none the wiser as to whether the 'real' colours of the set were chosen as some kind of ironic statement, or because those hues worked well when reduced to the monochrome of the television broadcast. It's also worth noting that Charles Addams' original cartoons were almost always monochrome. Either way, the colour image surfacing poses lots of interesting questions about our monochrome cultural memory from the days before colour technology.
John Brownlee at Co Design points out that, weirdly, the pastel hues of the set are very reminiscent of Tim Burton's 50s vision of American Gothic. In the 1993 Addams Family Values movie, Uncle Fester is coerced into a marriage and finds himself in a pastel-shaded hell not a million miles away from the
set below. So perhaps the real Addams Family mansion has, by happenstance or by design, successors despite its monochromatic fame?