Commercial curry powder was a British invention and is rarely used in Indian cookery (they make their own). It can be found in a range of flavors and intensities from sweet to hot. All are mixtures of roasted, ground spices, generally including turmeric (the source of the yellow color), coriander, cumin, fenugreek, ginger, nutmeg, fennel, cinnamon, cardamom, various peppers and, of course, curry leaves.
In south Indian vegetarian cooking the curry leaf is an essential element in their masalas (spice mixtures), which also include: black mustard seeds, cumin, fenugreek seeds, dried chilies, black peppercorns, coriander seeds and turmeric. I recommend that you toast the spices and make your own mixture (see spice section).