Grey component replacement

Within the CMY color space, a range of colors can be achieved by combining the three primaries. This combination in its turn can be thought of as a hue component (which will require a maximum of two primary colors) and a grey component (a mixture of all three, in an appropriate quantity to give the required saturation). If the grey component is replaced by black ink, the same color is being achieved by using two primaries and black. The act of substituting a quantity of black for the grey component is known as "Grey component replacement" (GCR).