Dust is seen everywhere throughout the image in brown hues. The darkest brown hues are lanes of higher particle density, which appear dark as the high-density dust absorbs visible light from background stars.

https://apod.nasa.gov/apod/ap090615.html

Author: Amanda Cattel, UCF Undergraduate 2017
Editor: Patrick Joiner, UCF Interdisciplinary Studies, Class of 2018
Senior Editor: M.M. Montgomery, Ph.D, UCF Physics