I know some people don’t like grackles. Of the 3 species in North America, they are all fairly common within their ranges. I don’t have feeders but apparently Common Grackles can be aggressive, which is why people often dislike them. They are also not always obviously bright and colorful.
But it all really depends on how you look at a thing.
Grackles are quite bright and colorful when our eyes, light, and their feathers align. Many colors of birds are due to pigments, actual substances in the feathers. Other colors are caused by the structure of the feathers, such as blues in Eastern Bluebirds or iridescence in grackles. Iridescence is not unique to birds, but here is how it works in the avian world:
“Iridescent colors are produced by differential reflection of wavelengths from highly modified barbules of the feathers that are rotated so that a flat surface faces the incoming light. The detailed structure of the barbule reflects some wavelengths and absorbs others, and the reflected wavelength changes with the angle of reflection. The structural color is registered by the eye in response to the reflected wavelengths and changes with the angle formed by the light, the reflecting surface, and the eye.” –Stanford University, Birds of Stanford, Essays, “The Color of Birds” https://web.stanford.edu/group/stanfordbirds/text/essays/Color_of_Birds.html
Or more simply:
“Iridescent feathers appear black or dull one moment, then flash into glittering color as light hits them at just the right angle. The colors are produced as the feather’s microscopic structure reflects some colors while eliminating others.” –The Cornell Lab of Ornithology, Bird Academy Handbook Chapter 4 “Iridescence: and the Birds-of-Paradise”, https://academy.allaboutbirds.org/iridescence-and-the-birds-of-paradise (Watch the video!)
It all begs the question: Is a grackle still colorful when you aren’t looking at it?