The following chart illustrates the effects that changing the color mode has
on the histogram of a static subject.
The subject was a row of various neon-colored bathroom cleaner containers, and
with some deep black ink, lit by tungstun room lighting.
The camera was a Canon 1Ds, in manual mode, set to JPG large/fine, with zero
sharpening.
It has been suggested that the JPG settings are applied to the thumbnail
which is shown on the camera's review LCD, and that the histogram is then
calculated from this thumbnail.
This effect is important to RAW image shooters who desire to expose as 'far
right' / as bright a scene as possible, to avoid image noise, and without
overexposing the highlights.
The five graph lines / color modes are as follows:
1 - natural-looking hue and chroma
2 - hue and chroma suitable for portraits
3 - hue and chroma similar to high-chroma slide film
4 - Adobe RGB
5 - low chroma (my understanding is that this is the camera's native color
space)
DEEP SHADOWS (the far left verticle line)
Option 3 puts a considerable number of pixels in the deep shadows, followed
by 1, 2, 5 and 4 with the least.
MID-SHADOWS (the first upward slope and peak)
High-chroma option 3 darkens this area the most, while Adobe RGB is the
brightest. Portrait-mode # 2 creates a peak considerably to the upper
right of the other options.
MID-TONES (the next two peaks)
The high-chroma option 3 peaks higher and more to the right in the darker
mid-tone peak, while the portrait mode #2 is shifted to the bright side.
UPPER MID-TONES / LOWER HIGHLIGHTS (the last peak, and
downslope)
This is the important part for those who shoot high-contrast scenes.
Low-chroma option # 1 is the darkest (thereby giving the most headroom to avoid
blown highlights), with Adobe RGB mostly overlaid, while the remaining three
color options are considerably brighter.
CONCLUSION
If you are having trouble with noise in the shadows, and blown out
highlights, shoot in color mode 4 or 5. If you are shooting under
controlled lighting, or need to retain / enhance fine gradations in hue, use one
of the other 3 options.