[old_tv_nut]

Actually, the major change was in the green, because the sulfide green was much yellower than original NTSC willemite green (oscilloscope P1 green phosphor). The red did change slightly when sulfide red was used, due to saturation and an orange shift at high beam current. Rare earth red brought the red back close to NTSC spec.

Blue was shifted very early (perhaps in some versions of the 21AX?) when sulfide blue was introduced. The sulfide blue was more violet than the blue in the 15GP22, and was closer to the blue that the RCA engineers really wanted. The 15GP22 used a non-sulfide blue because sulfide blue could be contaminated in the 15GP22 production process and turn green, and that got written into the NTSC specs.

So, the divergence from NTSC phosphor colors started early, with partial compensation by changing the color demodulation angles/gains/matrixing lagging behind. This never got fully fixed until PAL and HDTV adopted the modern phosphor set, which also transferred over to computer still images as part of the sRGB standard used in jpg.

The main loss of color gamut in modern displays compared to NTSC is in the cyan (blue-green) region due to the yellower green primary.