Turmeric is a unique spice, with a musky, earthy flavor that gives depth to curries and soups. Its rich yellow color is so brilliant that the spice is sometimes used as a fabric dye. There is no spice that is a reasonably close substitute for turmeric. However, it is often used as part of spice combinations such as curry powder, which won't be glaringly different if you simply leave out the turmeric.
Curry powders can be very simple, with mainly cumin, coriander, pepper and turmeric, or they can be more complex, with cinnamon, cardamom, fennel and fenugreek, among other spices. There is no single right way to make curry powder, and some curry powder recipes only include a small amount of turmeric, or none at all. When following a recipe that calls for turmeric as part of a curry spice blend, add a little extra cumin to balance the brighter, sweeter flavors such as cinnamon and cardamom.
Curry Powder Substitution
Because curry powder includes turmeric and takes its characteristic color from the spice, you can substitute the spice blend for the individual spice. However, if you substitute curry powder for turmeric in a recipe that calls for a combination of individual spices typically used in curry powder rather than the complete spice blend, you should use the blend as a substitute for all of the spices, rather than just the turmeric.
Substituting for Turmeric Color
Turmeric's color is its most distinctive feature. Its flavor takes the background to other curry flavors, but its color stands out and gives the blend its distinctive hue. No other readily available spice provides the same intense yellow, but other spices can partially stand in, providing some brightness and some gold. Saffron has more of an orange tint, but its tone is somewhat similar to turmeric. Annatto seed is also not an exact match, but it colors food a comparable orange-gold.
Turmeric on Its Own
Some recipes, especially African-based curries, use turmeric separately from other spices, as the main seasoning for a dish. Such recipes rely so heavily on the distinctive flavor of turmeric that it's better to wait until you have turmeric available than to make an inadequate substitution. Although it won't give precisely the same flavor, smoked paprika can provide color and muskiness, and mace can provide a pungent spiciness that is somewhat similar to turmeric.