Food for thought..... the only food fish in freshwater that has a kill spot are the varieties of shad. The other food fish species such as fathead minnows, shiners, yellow perch, young bream etc. do not have a kill spot. When painting these other species, would adding a kill spot be beneficial or hurt the natural appearance of the bait? Hmmmmmmm....... Remember..... Match the Hatch?
Bream and sunfish have a "kill spot" ...the ear....
Fathead minnows have a strong lateral line stripe that ends in a pseudo kill spot at the tail
Perch ...I would think that predatory fish would target the darker bars
Some shiners have a tail spot
However .... It could be interesting to fish lures with kill spots vs lures without to see if fish actively target a bold dot