Read the link to answer your last two questions and then some. ;) The first question I think you answered already more or less. If the red stuff wasn't red people might figure out that they're just buying sugar that they could buy much cheaper in a 5 pound bag. If they started making their own the companies that make and sell the red (and pink and clear) stuff would lose money. So the red stays in to make people think they're getting something extra for their money when all they're getting is sugar + chemicals.

Here is a link that might be useful: Should I Add Red Dye to My Hummingbird Food?

Plus all that already said, the main common reason for some people might be the red color , which is not needed for most hummingbird feeders are already red. Since hummers are attracted to the tiniest little thing that is red and they will check it out, it would be total overkill. So why take a chance on something that could harm these wonderfull creature,, please no red coloring!!!