I am occasionally ask why the outside of my cabinet doors are lighter than the inside. The answer is usually because they were painted with an Alkyd or Oil base paint. Alkyd or oil based paints will darken or amber over time. Absence of light accelerates this process so areas that don't get exposed to light will darken quicker. Quite often touch ups that are light in color when first applied will blend in over time. Using a high quality Alkyd will help but not eliminate this condition. The only way to completely avoid ambering is to use an Acrylic Latex Enamel, but make sure to use a premium acrylic and proper prep work, we have all seen cheap latex paints peeling off of old oil enamels. Benjamin Moores "Advance Waterborne Alkyd" brings together the best of both worlds, the levaling characteristics of an alkyd and less VOC's than most latex paints, it also ambers less than traditional alkyds. Proper surface preparation is also very important when changing from an oil to an acrylic. Now for some fun, tape a piece of cardboard to the back of a cabinet door and place it in direct sun for the afternoon and see how much the paint lightens when exposed to sunlight.