That's an interesting question; I hadn't heard about this before. Christ, what a rabbit hole.

I first checked Benjamin Gross' The TVs of Tomorrow: How RCA’s Flat-Screen Dreams Led to the First LCDs (University of Chicago Press, 2018), because I know Ben and respect his work, which says (on page 21) that "the military’s requisition of electronics materiel following the outbreak of hostilities in Korea prevented CBS from expanding color set production." That line pointed me to a few other references, notably R.W. Burns, The Struggle for Unity: Colour television, the formative years (IET, 2008), which goes into this in a lot of detail on pages 152-153. Essentially, on November 19, 1951, the Office of Defense Mobilization (ODM) asked CBS to conserve materials judged critical to the defense program. The next day, the National Production Authority (NPA) issued a formal request that invoked a "shortage of critical controlled materials" and explicitly said:

This order prohibits the manufacture of sets designed to receive color television, and items solely designed to permit or facilitate the reception of color television. The manufacture of color television for experimental, defense, industrial, and certain hospital and educational uses is permitted. In particular it seems that they were trying to preserve "steel, copper, and aluminium."

Burns notes that this is a very weird and "illogical" request, given that they did not direct CBS to preserve the commodities in question (which it could have done), but instead banned a very specific product, and of course CBS could have easily wasted those commodities on other "non-essential" products if it wanted to. But he says that CBS, perhaps in an effort to appear patriotic and compliant, did not challenge the order on any grounds and instead instantly affirmed its willingness to abide by it.

So that's the very basic answer. But this comes out of a really complicated context that both Gross and Burns discuss. Essentially, the Columbia Broadcasting System (CBS) was trying to push out a color TV set and system in the early 1950s, ahead of any other competitors. Its major competitor was the Radio Corporation of America (RCA), a much larger and more experienced electronics provider, that was working on its own color television and broadcast standards. CBS was essentially trying to get its foot into a new and emerging market as a "first mover," even though its technology and standards were, apparently, pretty inferior to what was being developed at RCA. RCA spent a year or more trying to get CBS blocked in the courts, and by the FCC, succeeding in stalling CBS. But it went all the way to the Supreme Court, who in early 1951 ruled in favor of CBS, opening up the path for CBS to finally produce color televisions to its own standard, which it started advertising for.

There are way more technical and legal weeds here than I want to venture into (I've hit the limit of my interest, in other words), but this appears to be part of the overall order, and the specificity of it about color television. Because CBS' appeared to affirm the NPA order almost simultaneously, there was an appearance that it was coordinated — that CBS had tried, in other words, to get its color television production banned, because that would give it an "off-ramp" to the industrial-legal battle it was involved in with RCA. This wasn't the case (they appeared simultaneous because, as noted, the ODM had contacted them a day earlier). There was also apparently a belief that RCA somehow got the ODM to shut down CBS' work, because RCA spent some time vigorously asserting that it had done no such thing (as did, oddly, the FCC). So there is a lot of this that appears to have been seen at the time as "extremely convenient" to both RCA and (somehow) CBS.

RCA continued developing color televisions (but not manufacturing them) during this time, and doing demonstrations and lobbying of its system, which got it a lot of positive attention since their set was much more impressive than CBS' once developed, and their standards for broadcasting with compatible with black and white receivers, which during the early 1950s had dramatically increased in production (the total production of black and white television sets from 1940-1948 was about 1.2 million, with almost all of that in 1948; by 1952, another 22 million had been produced), like CBS's system. All of these things, including the order which prevented (in practice) CBS from becoming a powerful "first mover" in this field, led to CBS eventually concluding to abandon its efforts and support the RCA approach.

Which is to say, there is the "official" reason, which looks a little fishy, and a more complicated context which suggests that this was part of an industrial rivalry between two companies. Interestingly neither Gross nor Burns really go "all the way" in asserting that RCA was (somehow) pulling the strings here, finding an excuse to shut down CBS' color television ambitions for a few crucial years so that RCA could shore up its technology and its standard (which would become NTSC and formally adopted in 1954). Perhaps there is just not sufficient evidence of this; perhaps it is a matter (as is clear in Burns' book) that a lot of different actors did not want CBS to succeed, and so knowing exactly how this went down is unclear and there are more possibilities here. But there is something a little fishy here, though the RCA victory is in all of these texts painted as a great engineering and commercial accomplishment that ultimately benefited the consumers way more than a CBS victory would have.