What part of the flower attracts pollenators?

Insect pollinators are attracted by the petal, and its colour first. Some bees and butterflies have four or more colour receptors in their eyes, (we have only three) and can see into the ultraviolet region, which we cannot. Scent also plays its part particularly if the plant 'wants' the insect to enter the flower.

Orchids are renowned for their curious fertilization mechanisms, and some even resemble female insects so the target insect will attempt to mate, thus fertilizing the flower. Other orchids such as the Pterostylis, have a slippery labellum which, when the insect lands on it, springs back, dumping the insect into the globular base of the flower, from where it has to climb out in such a manner as to fertilize the flower.