Final answer:
In aviation, the lavatory call light typically illuminates in red to signal that assistance is needed. Based on the theory of subtractive color mixing, the blue section of the color wheel looks blue by reflecting blue light, and the yellow section looks yellow by reflecting red and green light.
Step-by-step explanation:
The student has asked about the appearance of colors when light shines upon a subtractive color wheel. The light in question is a combination of red, blue, and green light. When discussing which part of the color wheel will appear blue, it's important to understand that the blue section will look blue because it will reflect blue light and absorb red and green.
Conversely, the section that will look yellow is the one that absorbs the blue light while reflecting the red and green light because yellow is the color created when red and green light are mixed.
Let's apply this concept to the question posed: the lavatory call light. This light commonly illuminates in red to indicate that assistance is needed. In the context of the subtractive color wheel, if red and green light shone on it, the red portions would reflect red, and similarly, the green portions would reflect green, while a combination of the two would appear yellow. Thus, if we consider standard aviation practice, the correct answer to the question 'What color does the lavatory call light illuminate?' is Red (D).