Hummingbird feeders should be filled with sugar water mixed at a ratio of one part white sugar to four parts water. This ratio approximates the sugar content of natural flower nectar and provides a good source of calories.
Plain white sugar is sucrose, which is the same kind of sugar predominantly found in flower nectar. It is the only type of sugar recommended for hummingbird feeders. Honey, molasses or brown sugar are not healthy alternatives. Honey also tends to ferment quickly, which can lead to the growth of mold. Red food coloring, while probably not harmful, does little to attract birds and is not necessary, since most commercial hummingbird feeders are made of red plastic.