Bees cannot see the color red - whatever about red flowers attracts them, it isn't the color. But they can see orange and yellow, and they swarm the feeders with these yellow guards on much more than my all-red feeder.  Maybe decades ago this color issue wasn't known, hence a tradition of cheery yellow bee guards developed, but come on, Perky-Pet -- get with it. Red or colorless bee guards make a lot more sense. btw, if you have woodpeckers or flickers that like to guzzle from the feeders, they can sometimes crack parts of the guards, letting bees get in anyhow.