It isn’t. It often is colored using the same colors that are used for shampoo.
But before getting added colors, conditioner is white, and opaque. It is white and opaque for the same reason milk is white and opaque. Like milk, it has tiny droplets of oils and fats surrounded by water. These droplets scatter the light that hits it, just like the droplets of water in a cloud do. We see the result as opaque and white.
Hair conditioner has several ingredients in it that each do their own task to condition the hair. Hair has millions of tiny scales on each strand, and if these scales stand up away from the hair, it makes the hair tangle more easily, and appear dull.
Acids, like citric acid, are added to conditioner because the acid makes the scales lie down against the hair.
Conditioner also has some detergents like shampoo does. But the detergents in conditioner are designed to stay in the hair. The water-loving end of the detergent sticks to the protein the hair is made of. The other end of the detergent is a long chain that sticks to oils and fats. This allows the detergent to hold onto the hair and the oil at the same time, so the oil coats the hair. This makes the hair shiny and helps prevent tangles.
One of the detergents used is panthenol, a precursor chemical to Vitamin B5 (pantothenic acid). It holds onto the hair protein, and also holds onto water. It coats the hair and makes it shiny, and also lubricates it to prevent tangles. It is sometimes called a provitamin, but it has no nutritive value when added to hair, which is just protein, and has no living cells.
Other anti-tangle ingredients are silicone based lubricants like dimethicone, and fatty alcohols (synthetic detergents made from oils). When you see stearyl alcohol, or cetyl alcohol, those are fatty alcohols. Cetearyl alcohol is a mixture of the two. They help make the conditioner opaque, in addition to their lubricating and stabilizing functions.