Question

Y-Y=(R+G)-(R+G)

Yellow light is allowed to pass through a yellow paper.

Answer 1

Yellow light consists of red light and green light. A blue pigment is capable of absorbing yellow light; that is, blue paper can absorb both red and green primary colors of light (recall that yellow light is a mixture of red and green light). So red and green light shine on the paper; and both the red and the green light must be subtracted. There is no color left to be reflected to the eye. Subsequently, the paper appears black.

Y - Y = (R + G) - (R + G) = No reflected light = Black