This is not necessarily correct. When I was doing testing with RA4 safelight intensities, there turned out to be quite a wide range of light levels where there was no fogging of paper whites, but a pronounced color cast that could not be filtered away entirely. The same is true for off-spec chemistry; there's a bandwidth where paper whites remain white, but color balance cannot be adjusted properly. HOWEVER, generally you move outside that bandwidth (both with light fogging and the chemistry issue) occasionally, resulting in seemingly isolated incidences of more visible problems that ultimately give away the problem. Still, don't rely on paper whites telling the full story with RA4. It's a good clue, but not the only one.