Colour adding

Two objects (for the sake of argument in the 1.9.1 preview grid) that produce light. One produces red light, the other yellow (red + green). What colour is the area light where they overlap (the lightpools on the floor, I know if I put something in there it will react differently on the different sides)?

I'm tempted to speculate orangey - you'd get effectively red + 0.5 green so redder than yellow, but I will admit I'm not great at these things in my mind's eye.

What you actually get is white - but where does the blue come from for adding to white?!

If the sun is down, there is some blue light being cast on the whole environment. This is to simulate darkness, because night in SL isn't pitch black. Its bluish.