The question of 3 vs 4 tube cameras was still an issue when the UK started its colour service in 1967. At least we had Plumbicon tubes rather than IOs. Hence no incentive to tray and match a single IO for Y with 3x vidicon for RGB. Or make a huge camera with 3x IO.
There were 3 cameras available in the UK in 1967. The Philips PC60 was 3 tube, the Marconi VIII and EMI 2001 were both 4 tube.
I think the Philips PC60 was sold in the US under the Norelco name. The Marconi VIII was widely sold internationally. The EMI 2001 saw little use outside the UK.
4 tube cameras gave better registration and grey scale. The problem of resolution on 3 tube camers was later solved by taking high frequencies largely from the green channel.
The other big argument was about constant luminance. Becuase all the RGB/YUV matrixing is performed on non-linear signals some Y travels in UV and vice versa. If Y and UV all had the same bandwidth this would hardly matter but they don't so you get various artefacts. 4 tube cameras got much closer to constant luminance than 3 tube.
In the early days in the UK, an EMI engineer called Ivan James was the main proponent of constnat luminance. I can see that I wrote almost the exact same post here in 2010:
http://www.videokarma.org/archive/in.../t-248163.html
See also Poynton whose explanations are pretty good:
https://poynton.ca/notes/video/Constant_luminance.html