The flowers typically have a delicate, sweet scent, which teh bees can smell. Usually the nectar is at the end of some type of small, narrow floral tube which is the right length to fit the tongue of the particular species bee that pollinates that plant. They can see red. Butterflies typically walk around on a flower cluster, probing the blossoms with their tongues. The individual flowers are typically tubular with a tube of suitable length for butterflies.
Most moths are nocturnal and have a good sense of smell.
Moth-pollinated flowers typically are white or pale colors so they will be at least somewhat visible on a moonlit night. Often, moth-pollinated flowers may only be open at night. Moths are hover-feeders, so these flowers have deep tubes to precisely match the length of a specific moth's tongue. One famous story relates that Charles Darwin found an extrordinarily long, tubular flower in South America and predicted that some day, someone would find a moth with a tongue of matching length. After much searching, around a hundred years later, indeed, this moth was found.