Do you know why snow is white?That is because it has forgotten what color it used to be. =Do you know why snow is white?That is because it has forgotten what color it was. = Do you know why snow is white?That is because it has forgotten its own past color.
Do you know why the snow is white? That is because it has forgotten its color. Do you know why snow is white? That's because it forgets which colour it was.