This is actually an extremely complex and interesting question.
How much of each colour depends on the wavelengths of the original red, green and blue sources.
For instance what optical wavelength is really green ?
If you had a variable frequency light source, and ask ten different people to adjust it to "perfect" green, you will have ten slightly different wavelengths, and a big argument.
Likewise red and blue. You can drift towards or away from the infrared, and it will still be red, or towards or away from ultraviolet, and it will still be blue.
TV camera sensitivities and CRT phosphors vary a lot in peak sensitivity and peak output.
There have been different standards proposed over the years in various countries but the whole thing has become a historic mess.
One of the original standards for colour TV was the CCIT chromaticity standard. I suggest you Google this to get a deeper understanding.
Black is pretty easy, but the number of different types of white paint available from a paint store, and they ARE different might convince you that true white is not so easily defined.
Back in my student days I leaned that the sensitivity of the human eye to various colours is:
Red 30%
Green 59%
Blue 11%
The eye being most sensitive to green, and least sensitive to blue.
In the end, you will have to decide for yourself if what you are looking at is really white light.
Hold a sheet of white paper against the background of this post and see what two very different whites look like.
