Color space

There are many colors that can be formed from combinations of the basic sets of colors that make
up each color mode, such as RGB (Red, Green, Blue) or CMYK (Cyan, Magenta, Yellow, Black).
But not all devices (monitors, presses, desktop printers) can reproduce all the possible color combinations
within each color mode. Therefore, there are sets of color-combinations within each
color mode that are customized for different devices and that you can use to make up the colors in
your images. You can think of these sets of color-combinations as color palettes. They also can be
referred to as color spaces, color gamuts, or color profiles.
When you use a set of color-combinations that is specially made for an image’s destination device,
your image should look better when it is reproduced that device. For example, if you erroneously
use a color space that is made for uncoated paper for an image that is going to be printed on glossy
paper on a printing press, you are allowing your image to potentially have many more colors than
can be reproduced satisfactorily on uncoated paper. There can be unpredictable results in this situation.
It’s better in this situation to use a color space that is specifically tailored to uncoated paper
printed on a printing press.

Before you begin working on an image, you can specify the color spaces (also called color profiles or
gamuts) for various types of images, such as RGB, CMYK, Grayscale, and Spot Color. This enables
Photoshop’s color management functions, which attempt to keep colors accurate across devices,
such as a monitor, a desktop printer, and a printing press.
To specify color spaces, choose Edit ➪ Color Settings (see Figure 1.17). If you are working on
images for the Web, the sRGB color space is a good set of RGB colors to work in because it resembles
the set of colors available for display on many monitors.
If you are working on images for printing on a sheetfed press on coated paper, you may want to
choose the CMYK color space U.S. Sheetfed Coated. Custom color profiles (color spaces) may also
be created and loaded.


The Color Settings dialog box

You can change an image’s color profile by choosing Edit ➪ Assign Profile or Edit ➪ Convert
Profile. Assign Profile uses a conversion method that pays more attention to keeping the color’s
numeric values the same and does not prioritize keeping the color’s appearance consistent from one
color space to another. Convert Profile attempts to keep the color’s appearance the same from one color
space to another and does not prioritize keeping the color’s numeric values the same.
Color management is not a perfect system. With that in mind, you may also choose not to use color
management by clicking the More Options button in the Color Settings dialog box, then selecting
Color Management Off in the Settings menu.

(Sourse. photoshop bible)