Everyone knows that red means danger, but how did purple become a cautionary color? At an EPA conference in the late 1990s, attendees nearly came to blows over color coding on the Air Quality Index.

Millions of Americas affected by wildfire smoke are focusing on the colors red, purple and maroon on the Air Quality Index charts. Red used to be the scariest color. Why did that change?

“Purple has the excitement of red, but the calmingness of blue,” she says, noting that while orange is also a secondary color, its red and yellow components share warm messaging. Fair.