Polychrome is the "practice of decorating architectural elements, sculpture, etc., in a variety of colors." The term is used to refer to certain styles of architecture, pottery or sculpture in multiple colors.
When looking at artworks and architecture from antiquity and the middle ages, people tend to believe that they were monochrome. In reality, the pre-Renaissance past was full of colour, and all the Greco-Roman sculptures and Gothic cathedrals, that are now white, beige or grey, were initially painted in bright colours. As André Malraux stated, "Athens was never white but her statues, bereft of color, have conditioned the artistic sensibilities of Europe... the whole past has reached us colorless." Polychrome was and is a practice not limited only to the Western world. Non-Western artworks, like Chinese temples, Oceanian Uli figures, or Maya ceramic vases, were also decorated with colours.
Ancient Near East
Similarly to the ancient art of other regions, Ancient Near Eastern art was polychrome, bright colours being often present. Many sculptures no longer have their original colouring today, but there are still examples that keep it. One of the best is the Ishtar Gate, the eighth gate to the inner city of Babylon (in the area of present-day Hillah, Babil Governorate, Iraq). It was constructed in 575 BC by the order of King Nebuchadnezzar II on the north side of the city. It was part of a grand walled processional way leading into the city. Its colours are as rich as they were back in the day because of the fact that the walls were made of glazed brick.
Many Ancient Near Eastern sculptures were painted too. Although they are grey today, all the Assyrian reliefs that decorated royal palaces were painted in highly saturated colours.
Ancient Egypt
Thanks to the dry climate of Egypt, the original colours of many ancient sculptures in round, reliefs, paintings and various objects were well preserved. Some of the best preserved examples of ancient Egyptian architecture were the tombs, covered inside with sculpted reliefs painted in bright colours or just frescos. Egyptian artists primarily worked in black, red, yellow, brown, blue, and green pigments. These colours were derived from ground minerals, synthetic materials (Egyptian blue, Egyptian green, and frits used to make glass and ceramic glazes), and carbon-based blacks (soot and charcoal). Most of the minerals were available from local supplies, like iron-oxide pigments (red ochre, yellow ochre, and umber); white derived from the calcium carbonate found in Egypt's extensive limestone hills; and blue and green from azurite and malachite.
Besides their decorative effect, colours were also used for their symbolic associations. Colours on sculptures, coffins, and architecture had both aesthetic and symbolic qualities. Ancient Egyptians saw black as the colour of the fertile alluvial soil, and so associated it with fertility and regeneration. Black was also associated with the afterlife, and was the colour of funerary deities like Anubis. White was the colour of purity, while green and blue were associated with vegetation and rejuvenation. Because of this, Osiris was often shown with green skin, and the faces of coffins from the 26th Dynasty were often green. Red, orange, and yellow were associated with the sun. Red was also the colour of the deserts, and hence associated with Seth and the forces of destruction.
Later, during the 19th century, expeditions took place that had the purpose of cataloging the art and culture of ancient Egypt. Description de l'Égypte is a series of early 19th century publications full of illustrations of monuments and artifacts of Ancient Egypt. Most are black-and-white, but some are colourful, so they can show the polychromy from the past. In some cases, only a few traces of paint remained on the walls, pillars and sculptures, but the illustrators attempted successfully at showing the buildings' original state in their pictures.