Humans can perceive yellow light because, when the light hits the back of the eye, it stimulates both "blue" and "green" cones. how is this fact related to the fact that one type of odor molecule often stimulates several types of receptors?

perception of color and odor are created by combinations of the receptor types

The perception of color and odor is determined by the combination of the receptor that catches the stimuli. That is why there is a wide variety of stimulus that can be perceived by such sense. if the perception coded by a specific receptor, the organ will need much more receptor that will make it less sensitive.