I've read of boiling the nectar. I don't. Never have. Nor do I put in red food coloring. I've been feeding hummingbirds every summer for years, cuz they're here all summer, from mid May till Labor Day weekend. And noisy they be - their chips and high pitched humming sound is heard from afar!
So how I mix my sugar water works. I just use hot tap water and stir till sugar is dissolved.
Hummingbird Nectar-1 part sugar
-4 parts water
(So 1C sugar to 4C water is my typical amount I'll make up)
-Have part of the water hot tap water till sugar dissolved, then add the rest as cold water.
I'll use this filling time to rinse the feeder in the hot tap water too. I do have a bottle brush for feeders if need be.