There are a number tactics folks employ to deter bees, yellow jackets, and wasps from their feeders. Here is one you may not have considered: avoid using feeders decorated with yellow features.
Most often, yellow is used to decorate the artificial flowers surrounding feeding portals. I am not sure why manufacturers go to so much trouble to include yellow in the color scheme of a feeder. Perhaps they feel yellow flowers look more realistic, or attractive. Who knows? One thing we do know is hummingbirds are attracted to the color red found on such places as the feeder base and top. As such, using yellow on a feeder does not enhance the chances that hummingbirds will use it.
When yellow is used to decorate a feeder, it simply makes the feeder more appealing to bees, yellow jackets, and wasps. The reason for this is honeybees, wasps, and yellow jackets are attracted to the color yellow. Consequently, in theory, feeders that do not feature the color yellow should not be visited by these insects as often as feeders without the bright color.
However, if red feeders are coated with sugar water that has sloshed out of feeder portals, squadrons of these stinging insects will most assuredly show up. In addition, these flying insects are capable of finding a source of food regardless of whether it has any yellow on it or not. I know this is true as just last week I was stung by a yellow jacket as I tried to refill one of my red feeders.
Using feeders without yellow will not solve the problem of hummingbirds having to share nectar with hornets, honeybees, and yellow jackets. However, it just might help alleviate the problem.