The Meccan Revelations: Page 121 from Volume One

Among that is the sphere of ether and its spirit is heat and dryness, which is the sphere of fire and its counterpart is yellow and its spirit is the digestive force. Among that is air and its spirit is heat and moisture and its counterpart is blood and its spirit is the attracting force. Among that is water and its spirit is cold and wet and its counterpart is phlegm and its spirit is the driving force. Among that is dust and its spirit is cold and dryness is its black counterpart and its spirit is the holding power. As for the earth. There are seven layers of black earth, dusty earth, red earth, yellow earth, white earth, blue earth, and green earth, corresponding to these seven layers of a human being: in his body is skin, fat, flesh, veins, nerves, muscles, and bones.