Red is widely considered to be the first colour used by early humans, in the form of iron oxide-rich ochres dug from the earth. It is connected with strong emotions and signals danger, an association shared across cultures – around the world, red is the most common colour used for warning and stop signs. Throughout history, artists have used red pigments gleaned from a variety of sources. Modern developments in organic and inorganic chemistry have now seen the red pigment family become one of th

President Donald Trump concludes his summit with Chinese President Xi Jinping in South Korea, his last stop on his weeklong trip to Asia. | NBC News

WATCH: President Trump shakes hands with Chinese President Xi after their historic meeting in South Korea. | Fox News