Which spice gives many curry powders their yellow color?

Turmeric gives many curry powders their characteristic yellow color.

Turmeric is the dried and ground rhizome of Curcuma longa, a flowering plant in the ginger family. Its intense golden color comes mainly from curcumin, a group of yellow-orange pigments concentrated in the rhizome. Curry powder blends vary widely, but turmeric is commonly included both for its earthy, slightly bitter flavor and for the bright color it contributes.

Curry powder is not a single traditional recipe and should not be confused with every spice mixture used in South Asian cooking. Commercial blends may also contain coriander, cumin, fenugreek, black pepper, ginger, cardamom, cinnamon, or chili. In fact, many regional Indian cooks prepare fresh spice combinations rather than using a standardized powder. Western-style curry powder emerged as a ready-made blend marketed to British consumers; one early commercial product was advertised in London in 1784.

Turmeric is also used as a food coloring outside curry dishes, including mustard, rice, sauces, and some dairy products. Saffron can create a similar yellow appearance, but it is not the usual coloring spice in ordinary curry powder.