Applying the Food Coloring
Apply the food coloring to the food a few drops at a time, stirring after each application until it reaches the desired color. Food coloring should be dispersed evenly throughout the food it is coloring. Only when it is mixed thoroughly into a dish can the food coloring's molecules can do their job. Food coloring is essentially made up of molecules that are formulated to absorb certain wavelengths of light, called photons. The molecules are so efficient that, when added to food of a different color, they can either trump or alter the original shade of the food.
How Food Coloring Works
When a concentrated food coloring molecule encounters the photon that it is designed to absorb, the molecule changes in that the electrons are excited by the photons. The electrons shift to another quantum level, using up the photon's energy in the process. The dye molecule is then left in an excited state. When the photon's energy is all absorbed, the electron releases the photon's energy as thermal energy and returns to its original quantum level. The photon has disappeared at that point, but is quickly replaced by another wavelength of light.
Working With the Food
Food coloring appears to change the color of food in that it alters the type of photon that the food is designed to absorb. Food coloring also allows a food to appear more vibrant in color because the dye's molecules are so densely packed and efficient. The reason why it must be distributed thoroughly in a food is because it must completely coat the surface of the product it is working with to do its job. Any areas left untouched by the food coloring will continue to absorb their pre-food-coloring photons. Food coloring, obviously, cannot be removed from food once it is added unless the molecules are diluted and spread out by adding more ingredients to the mix.