At times, it is a trick question; the question may be telling rather than asking.
Who is buried in Grant’s tomb?
The answer should be obvious. However,
what color of light is passed by a blue filter?
may seem obscure. The answer is obvious. We see it, and call it that color, because of the light that is passed or reflected by that thing. Blue is blue, because there is blue light present. No blue light, no blue sensation.
you convert one color to another.