First Ad for color in 4/26/1954 Life Mag.

[Electronic M]

Westinghouse H840CK15. I own the one that was auctioned in Portland in 2020.
Westinghouse beat the CT-100 (also have one) to market by over a month. Admiral beat them both by a decent margin, and it's possible that Raytheon was the actual first claiming you could order their color set in December of 1953 (within something like a week of NTSC color being standardized).

The one thing RCA could claim with the CT-100 is the first MASSPRODUCED color TV....They made 4-5K of them on an actual assembly line as they would a volume selling monochome set. All the other 15" 1954 color sets, and even a good chunk of NON-RCA color between 54 and 61 were hand built because a production run of 10-500 didn't warrant tooling up an entire production line.