because white is a dull colour its very blank it is not used in most drawings White is the lightest color and is achromatic (having no hue). its the opposite of black.so as barren lands are barren and the colour white is blank it is used to represent barren lands.
hope it helps i searched the answer as much as i could but i could not find an appropriate answer so i just thought of this
6. contain abundant clouds of cool gas and dust --- Spiral galaxies.
7. have significant, ongoing star formation --- Spiral galaxies
Explanation:
Most galaxies that contain a central bulge that is surrounded by a rotating disk of arms that circles the galaxies are said to be a spiral galaxy.
About 60% of the galaxies are made up of spiral shapes and they are mostly found n low-density regions and are in the central of the galaxy clusters. Spiral galaxies often have beautifully shaped made form hot and young stars.
The more reddish in color indicates much older galaxies and are resemble that of an elliptical shape. Also, they consist of a little amount of dust and gas left. Spiral galaxy has rich gas and high star formations.
