Final answer:
When a substance is excited with blue light, it will emit or appear orange, as orange is the complementary color to blue on the color wheel. This is based on the information provided that materials absorbing blue light appear orange.
So, the correct answer is: orange.
Step-by-step explanation:
The color that will be emitted when a substance is excited with blue light depends on the specific wavelengths of light that the substance absorbs.
If the material absorbs blue light, which has a wavelength range from about 450 nm to 495 nm, it will likely reflect or emit light in the orange part of the spectrum.
This happens because the complementary color to blue is orange on the color wheel, so when blue light is absorbed, the color seen or emitted is often its complement. In the context of the color spectrum that goes from red to violet, the emission spectrum of a substance excited by blue light would show a shift towards the colors with longer wavelengths than blue, such as green, yellow, orange, or red depending on the specific properties of the substance.
However, based on the provided information that materials absorbing blue light appear orange, the correct answer to the question is orange.