The correct answer is option 'C', which states that the colours used for Harappan pottery were shades of red, pink, buff, and sometimes black.

The Harappan civilization, also known as the Indus Valley civilization, was one of the earliest urban civilizations in the world, flourishing around 2500-1900 BCE in the region of modern-day Pakistan and northwest India. The people of this civilization were skilled in various crafts, including pottery.

The pottery of the Harappan civilization provides valuable insights into their culture, lifestyle, and artistic abilities. The colours used in Harappan pottery were primarily derived from natural pigments, which were applied to the clay vessels before firing. These pigments were obtained from various sources, such as minerals, ores, and vegetable matter.

Here is a detailed explanation of the colours used in Harappan pottery:

- Shades of Red: Red was a prominent colour in Harappan pottery. The potters achieved this colour by using iron oxide, which is naturally reddish in color. The red pigment was applied either as a solid coat or in combination with other colours, creating intricate designs and patterns.

- Shades of Pink: Pink was another commonly used colour in Harappan pottery. The potters achieved this hue by adding a fine powder of manganese oxide to the clay. The presence of manganese oxide in the firing process resulted in a pinkish tone in the pottery.

- Shades of Buff: Buff refers to a light, yellowish-brown colour. It was also used in Harappan pottery, giving a warm and earthy tone to the vessels. Buff colour was achieved by using various natural pigments, including ochre and other iron-rich minerals.

- Sometimes Black: While the primary colours used in Harappan pottery were shades of red, pink, and buff, black was occasionally used as well. The black colour was achieved by adding carbonaceous materials, such as charcoal or plant ashes, to the clay. Black pottery was relatively less common but was still present in the Harappan ceramic repertoire.

Overall, the colours used in Harappan pottery were derived from natural pigments and provided a diverse range of hues, including shades of red, pink, buff, and sometimes black. These colours not only added aesthetic appeal to the pottery but also reflected the artistic skills and cultural preferences of the Harappan civilization.