Blockx Venetian Red

Isn't it perfect that the opposite color of the earth is the color of the sky.
Opaque Red Iron Oxide, the most common earth element is opposite the sky color Cyan (Pathalocyanne).

Red Oxide, Venetian Red, Indian Red, English Red, all are darker hues of Cadmium Red which is opposite Cyan. These opposite colors mix to make a neutral dark.

Other sky colors like ultramarine blue and cobalt blue also mix nice neutral darks with red oxide or brown oxide.