The link to appetite regulation is from olfactory (and probably pheromonal) stimuli directly to the diet-responsive (and probably pheromone-responsive) hypothalamic neurogenic niche that controls nutrient chemical acquisition via its control of the dopaminergic and serotoninergic neuronal systems
Classical conditioning links sensory input directly to changes in hormone-driven behavior. Operant conditioning links the rewards associated with the behavior to behaviors that are repeated, or not. We can think about which behaviors we don’t want to exhibit or don’t want to repeat.
There is no direct link from visual or auditory stimuli that would explain any likelihood that spectral stimuli could classically condition the response to nutrient chemical associated with food odors.
I’ve dismissed evolutionary theory that involves random mutations, and used the epigenetic effects of olfactory/pheromonal input on OR variants, which provide a clear evolutionary trail that can be followed from unicellular organisms to insects to humans,
The honeybee is an invertebrate model organism that exemplifies the vertebrate molecular mechanisms of evolution via pre-existing genetic variation, not random mutation, that are detailed here.
Why is our response to other people enhanced by nudity? In other species with eyes, their visual response is enhanced by olfactory/pheromonal input.