Final answer:
In a faint green light, a red shirt will appear black because it cannot reflect green wavelengths of light and there is no red light present to be reflected.
Step-by-step explanation:
The perception of color depends on both the object's absorbance and reflectance properties and the color of the light shining on it. A red shirt appears red under white light because it reflects red wavelengths and absorbs other colors. In a room lit by faint green light, the red shirt will not reflect the green wavelengths and, with no red light to reflect, it will appear black or disappear against a black background. This phenomenon occurs because each color object has its unique reflective characteristics, which means that it will only reflect its own color and absorb all others. Since the red shirt can't reflect green light, it absorbs it, thus appearing black in a green-lit environment.