The Family DuMont

[jr_tech]

White P-4 phosphor on early CRTs is actually a mixture of two different phosphors. One component is yellow and the other is blue. Combined in the correct ratio the mix produces a decent, fairly uniform white.
Sometimes I have observed, when re-installing a round P-4 CRT after work on the chassis, that orientation of the CRT is critical otherwise "blueish" areas of the CRT are illuminated. I suspect that the blue component of the P-4 phosphor ages more rapidly, and over time the used areas of the tube become "warmer" or more yellow. Likewise, I would postulate that a new P-4 CRT would very likely be bluer than a well used one.
jr