In the cinema we can sometimes see the events in the film as if they lay behind the screen and it were transparent, rather like a pane of glass. The glass would be taking the colour away from things and allowing only white, grey and black to come through. (Here we are not doing physics, we are regarding white and black as colours just like green and red).—We might thus think that we are here imagining a pane of glass that could be called white and transparent. And yet we are not tempted to call it that: so does the analogy with, e.g. a transparent green pane break down somewhere?
We would say, perhaps, of a green pane: it colours the things behind it green, above all the white behind it.