Golden Rod and Vespid wasps (Ptera Hunter, Salem IL, 2006). Yellow attracts many pollinating insects, including these vespid wasps. Bees and wasps have trichromatic vision (three pigments), but they are not the same visual pigments (opsins) that we have. They can see farther into the ultraviolet but less well in the reds. Their clue to finding the sweet spot on a flower laden with pollen and nectar is their recognition of the yellow of the flower and its color patterns in the UV.
Flowering plants have evolved an interdependence with trichromatic pollinators. Many plants obligingly have co-evolved intensely yellow pollen to lure the pollinators to their nectar. Like many plants, this goldenrod takes its advertisement one step further; it makes its entire flower yellow. This splash of yellow taps into fixed-action patterns in pollinators who are drawn to the color. The signal is honest because there is nectar for the pollinators. However, the size of the reward may not be as advertised. The wasp will still get a pollen reward for its attention to the flower, but it could have had a more productive day had it not partnered with such a braggart.