|Female broad-tailed hummingbird (U. of Georgia)|
Here is why the people at The Birding Wire say you should not dye it red:
• It has NO purpose - Most hummingbird feeders you can buy have enough red color on them to attract hummingbirds without the need for red dye in the nectar. If there is no red on your feeder, simply tie a piece of red flagging, rope, or fabric to it.
• Red dye is typically petroleum based - The dye in colored nectar is red dye #40. Red dye #40 is now made mostly from petroleum, which is not good for any animal to ingest!
And a couple more. Read the whole thing.
Besides, the sugar water comes in handy when you need to make a quick Birder's Margarita.