A color space is a three-dimensional model of color. Red, green, and blue are placed on the three axes according to the chart below. RED on Horizontal Axis (X), Green on Vertical Axis (Y) and Blue on Z-Axis. The COLOR SPACE represents all of the possible colors.
But the devices in a photography system may not be able to display or print all of the colors. This is one of the basic truth that all devices can only show/handle some set of colors out of the whole COLOR SPACE.
The portion that a device can use is called the COLOR GAMUT. Color Gamut of one device varies from other and most of the times, they are not sub-set or super-sets of each other.
Please have a look at the image below and area in the triangle below shows Color Gamut of a particular Device. If a color in a file is not a color within the gamut then the color is called out-of-gamut. Then two approaches are followed to show out-of-gamut colors, We shall take this later.
In practice, the term color space is often substituted incorrectly for color gamut. From here on, color space will be used incorrectly to refer to the color gamut.There are two commonly used color spaces - sRGB & AdobeRGB. We shall talk more about sRGB and AdobeRGB in next article.