If you choose, you may add a drop or two of red food coloring to
the liquid. There’s no scientific evidence that the red food coloring
is harmful to the birds and the red color sometimes makes it easier to
see when your feeder needs to be refilled. Whether or not to use red
food coloring is a matter of your personal preference. Once they
discover the feeder, hummingbirds will feed just as readily from
feeders whose sugar solution is not colored in any way