A smaller percentage of a color equates to a smaller amount of color available to the pixel. Red may have a low percentage of cyan, high percentages of magenta and yellow, and no black. Colors in the CMYK mode are created by assigning a percentage to each color channel. Notice however that these shades of RGB differ from those in the image of RGB color. This is due to the difference in the way CMYK interprets and creates color.
Printers use the CMYK color system.
But because of the difference in the way monitors see color and printers do, you can get surprises when you go to print. This difference is in part due to the nature of the mediums, and in part due to your graphics adapter. Using higher quality adapters will lead to less surprises. Indexed Color Indexed color is for RGB images only, and refers to the overall color palette created for the image. Creates a palette based on the exact colors of the image.