Sorry za moje lenistwo, kolejny cytat:
"Now that you know what the histogram
is showing you — the number of pixels at
each luminosity level from 0 (black) to 255
(white) — and you know that the histogram
shows you a greyscale average because there
are no separate Red, Green and Blue (RGB)
histograms displayed, you need to be able to
understand how the camera evaluates color so
you can bias your evaluation of the histogram
depending on the color balance in the scene.
If the scene has a good balance of Red, Green
and Blue (RGB), there will not be a problem,
but quite often you will find yourself in situations
where one color predominates, or the
color balance is skewed in a way that favors
one color over another."
Najważniejsza nauka z tego cytatu to że pokazuje on (histogram) SZARY ODPOWIEDNIK nasycenia światła (luminosity) koloru wyrażonego jako RGB.

A teraz będzie ciekawiej ;-) :
"This sort of thing is not learned in a day,
so it will require some study, but once you
have a good feel for the way colors equate to
greyscale equivalents, you will find that you
can closely estimate how far below the right
margin (255) you need to set the exposure
to get correct saturation for a specific color."
I sedno sprawy:
"To expose 255 Red to full saturation
with no other color present, you should see
a spike at 64 grey." 64 grey to patrząc na histogram koniec I części !! dlatego tak łatwo jest przepalić niektóre kolory jako mieszanki RGB.