Which decade of the 20th century had the best colour film?

For my money, it was the 50's. The 40's, to me, are best remembered for the great black and white films. The 40's are a close second, though-Alexander Korda and Powell and Pressburger made gorgeous color films. The movie studios were trying to compete with television during the 50's so they went all out with epic stories and glorious color.

As interesting as I find the question, I'm not sure it can have a definitive answer from either an objective or subjective viewpoint; there are so many variables involved.

From 1932 on through the '50s, origination on Eastman Kodak negative stock to the specifications of Technicolor's three-strip system, and dye transfer prints manufactured therefrom, represented the gold standard. And until Eastman's introduction of its "monopack" system in the '50s, it was the only game in town outside of budget systems like Cinecolor or Trucolor. All things being equal, there should be no difference in quality between one struck in 1935 or 1955. But all things were not equal.

On the technical side, Eastman Kodak and other manufacturers of negative and positive stock were continually tweaking, making improvements in emulsion photosensitivity, grain structure and so forth, and optical companies were making their own improvements in lenses, for instance. There are those who feel that the industry-wide adoption of cellulose acetate "safety film" in the '50s replacing highly flammable nitrocellulose-based stock compromised image quality. Issues affecting print manufacture, such as color timing, are brought to bear upon what's seen on the screen as well. And that's all strictly within the photochemical realm, without getting into latter-day matters like digital restoration.

On the production side, variations in lighting, art direction, costuming and even makeup (skin tones being among the most reliable and readily discernible measures of color fidelity) have effects upon what a given viewer might judge as color quality or accuracy.   

And of course, "best" is completely subjective to begin with. Is it the most vivid? The most lifelike? The most artistic, or subtle, or...?  

I'll say this much: however technically accurate three-strip Technicolor may have been at realistically reproducing the color record of what was actually photographed, it introduced a quality that I'd call "hyper-realism:" it was almost too much. But for the best balance of vividness, realism and lifelike clarity, I'd point to films produced by Paramount in the '50s in their VistaVision format, which utilized 35mm film in three-strip Technicolor cameras specially manufactured to transport it past the lens horizontally rather than vertically, exposing a frame twice the size (8 perforations wide) of standard 35mm (4 perfs high), yielding a film image of unsurpassed detail, which in turn more finely defined color perception. 1955's To Catch A Thief is an outstanding example.       

I love 1950s Technicolor productions. The colours are so vivid.