formulas of Color gredient in ArcMap

For my thesis I need to find out the mathematical formulas of color gradient of Arcgis. Example: in a buffer which mathematical equation is used to represent the color transition from one color to another. I will use them to display buffer with different color and I need to have in mind all parameters graduation.Also what other equations exist for implementation of the color classification for square or other shapes. A good example is on this page How to Calculate Color Gradient (www.ehow.com), but this example is general I would prefer something that concerns the Arcgis.
Also the calculation of the gradient is different for points and different for polygons or a circle.