Short read (not looking thoroughly). Here's what I think: to allocate a region with the desired color. (there is an example of a football player, stands a rectangle of green grass, the result will be highlighted in all green color).
Solved: moving from RGB model to HSV. In the first model the intensity depends on three parameters, two-dimensional picture so hard to build. Often RGB is converted into the gray levels. At HSV you could take one coordinate of the hue (hue), but for two-dimensional pictures added saturation (saturation).
In Matlab there is an example
of the transition of RGB -> Lab, where the color is the two coordinates (a, b).