A white object emits white light that contains all the colors of the visible spectrum. What color is the image of the white object seen as after the light from it is transmitted through object A and then reflected from object B.
In our diagram, we see all this going on. We see the white light containing all the colors of the rainbow coming off of a white object. And this light is incident on an object called object A. Some of the light, certain colors, passes through object A and then makes it to object B. Considering this object B, we see that if all the colors of the rainbow, red, orange, yellow, green, blue, indigo, and violet, were incident on it, then a certain subset of those colors, we see three of them, blue, green, and yellow, will be reflected off of it.
So, here’s what we want to figure out. If light from this white object is incident on object A then makes it through object A and bounces off object B and then our eye is there to see the color of that light, what color would we see? What we’re basically trying to figure out is what color of light is both transmitted through object A and reflected off of object B? It’s that color that an observer there will see.
So, we start out by answering, which colors will be transmitted through object A? We see three colors, red, orange, and yellow. In other words, if object A and object B were arranged this way, and white light would shine on object A, then only these three colors, red, orange, and yellow, would actually make it to the surface of object B. The question is which, if any of these colors, does object B reflect?
We see the answer to that question from looking at the colors that B reflects. Object B reflects blue, green, and yellow light, which means that we do have a color of light that is both transmitted through object A and reflected off of object B. That color, and there’s only one of them, is yellow. If an observer was placed to see the light transmitted through object A and reflected from object B, the light the observer would see would be yellow.