Final answer:
Yellow light is formed by the mixture of red and green light, which is an example of additive color mixing. When red and green lights are shone onto a white paper, the light mixes and the paper appears yellow because red and green light combine to form yellow.
Step-by-step explanation:
The question is asking which two colors of light mix to form yellow when shone through a filter. Based on the given scenarios and understanding of color mixing with light, we can deduce the correct answer. When white light is shone on a yellow paper, the paper appears yellow because the yellow pigment absorbs all the other colors and only reflects yellow. However, if yellow light shines on a white paper, the paper appears yellow because the white paper reflects all colors and the source is only emitting yellow light. When red and green lights shine on a white paper, the combination of red and green light makes yellow. This phenomenon is known as additive color mixing where different colors of light combine to form other colors.
Regarding the color wheel and the behavior of colored light, color and color vision principles tell us that a blue filter will absorb all colors except for blue itself. When red, blue, and green lights are used, parts of the color wheel that are complementary to these colors will appear in the respective subtractive color, due to the absorption of the specific light frequency and reflection of the others. For instance, yellow absorbs blue light and reflects red and green, which mix to make yellow seen by the observer. Therefore, the correct answer to which two colors mix to form yellow is red and green (a).