Universally accepted colour for mountains is:

The correct answer is Grey.

Key Points

• Brown is commonly used to represent mountains on maps, as it signifies the rocky, rugged terrain typically found in mountainous regions.
• Mountain ranges, especially in regions like the Himalayas or the Rockies, often have greyish, rocky surfaces due to the nature of their geology.
• The Brown color also conveys a sense of coldness and harshness, often associated with mountainous environments.
• In map and geographical representation, brown serves as a neutral tone that doesn't distract from other topographical features, such as rivers and forests.

Additional Information

• Mountains are typically formed through tectonic processes like the collision of tectonic plates, volcanic activity, or erosion, which gives them a rugged, rocky appearance.
• Snow-capped mountains may sometimes be shown with white, but the base color is usually Brown to represent the rocky surface beneath the snow.
• In art, literature, and popular culture, grey is also used to symbolize the challenging, imposing nature of mountains, which often represent isolation and strength.
• The use of snow white, dark green, or brown for mountains can occur in specific contexts like artistic representation or environmental depiction.