What effect does the nitrate ion have on the color of the flames?

Answer 1

None. Using flame spectral analysis, we can use a prism or other device to determine the color of various metals. Nitrate gives no color. The purpose of the test is to give metal detection, qualitatively. Testing for nitrate is another test, not involving flame.

Answer 2

The nitrate ion usually enhances the intensity of the flame color by acting as a source of oxygen. It can form different colored flames depending on the metal it is combined with.