Gamma Correction and Color Space

Gamma does not affect the representation of a color in all color spaces equally and has no affect on color representation in many color spaces. (A color is represented in a "color space" as a set of coordinates (R,G,B = 255,255,255) for example. The are many different color spaces commonly used. Each is a 3 or 4 dimensional coordinate system used to express color information.)

Below are two lists of color spaces. The colors listed as device dependent are functions of the "system gamma" used. The colors spaces listed as device independent are not a function of gamma at all.

Device Dependent Color Spaces

Device Independent Color Spaces

Brightness

The greatest effect of Gamma on the representations of these colors is a change in overall brightness.

To see this visually using Adobe Photoshop, change the Gamma setting in the Monitor Setup (File Menu -> Preferences -> Monitor Setup). An image in RGB space should become lighter as you raise the gamma setting and darker as you decrease the gamma setting. An image in Lab space (Photoshop calls this Lab Mode) should not be affected by gamma. Some earlier versions of Photoshop may not support Lab color space.

Color or Hue

A change in gamma can also effect hue of a particular color representation. For example, the color below, represented in RGB space has 80% Red, 20% Green and 20% Blue, or 8:2:2 ratio.

However, if that color is not gamma corrected properly the ratios between red, green and blue will change. The color below simulates the above color with gamma correction of 1.0. The new ratios are 32:1:1

I say the gamma correction is simulated, because your browser has no notion of gamma correction and therefore I can't tell it that these two colors need different gamma correction. Even if your browser did no about gamma, and know what to do with it, the JPEG and GIF formats do not store gamma. The colors were made in Adobe Photoshop in Lab color space and converted to RGB space using the gamma mentioned. 
                                
            Gamma Correction = 1.0         Gamma Correction = 2.5
          Source           Output         Source             Output
           R 80%            R  57%         R 80%              R 80%
           G 20%            G  ~0%         G 20%              G 20%
           B 20%            B  ~0%         B 20%              B 20%