While the buds have been cut off, but still contain some moisture, just like a cut flower in a glass of water, it will continue to live for a little while.
Storing it with a little moisture, but in the dark, allows for no more new green chlorophyll to be produced. And the plant’s own cellular function, as well as some microbes will continue to break the chlorophyll down, as long as there is some moisture.
This is why people let the plant dry a little, but not all the way dry, and then put it in a airtight container, and then open the container top to let a little moisture out every now and then.
Things can’t get too moist or you’ll get mold and rot.