Lutein (Halloween Carotene)

Lutein is just another carotenoid - like the previously covered retinal, it is a terpene.

Long, huh? That chain of alternating double and single bonds affords it its wonderful color. It, like retinal, plays a role in vision. The halloween angle is because it's one of the pigments in your pumpkin making it orange. The brilliant oranges and rust colors you see in nature tend to be thanks to carotenes.

In fact, as the leaves are changing (although it's not a great fall for this in much of the US), you're seeing the carotenes show their color as the chlorophylls fade away. In this beautiful image below, you can see the parts of the leaf near the central veins still have their chlorophyll, while the parts a bit further away are starting to fade and show the brilliant carotenoids (which were there all along, just masked by that showy chlorophyll!). There's also, no doubt, some anthocyanins in there.