Add the sugar, and stir the mixture until it boils again. Boiling helps keep the mixture fresh longer. Make sure the mixture is cool before using it in your feeder. Store what's left in the refrigerator. It is not necessary to add red food coloring, as long as some part of the feeder itself is red.
Some people wonder if all that sugar can be good for the birds.
Actually, this recipe is similar to the nectar naturally found in flowers. During a display dive, their wings can beat up to 200 times per second. They take about 250 breaths per minute. Their hearts beat about 1,260 times per minute. They have 1,500 feathers.