=Bob wrote:
>   Okay, I lined up the spheres perpendicular to the light and now see what you
> mean. I should have done that before.
>   About the boxes, I removed the same-surface effect by scaling one of them
> slightly larger in the z direction.
>   No merge problem so it appears. Except...
[snipped code]
> I tried increasing color intensities above 1 with no change too. I would have
> expected to see magenta. Any ideas?

I agree about the merge problem (or lack thereof) - the cutout where the
surfaces overlap is more a "behaviour" than a "bug", and any POV-Ray
user with CSG experience knows little extra dimensions here and there
are par for the course.  At any rate, on POV-Ray for DOS a scale of <1,
1, 1+1e-14> to either box removes the problem, and if precision of that
order can't be considered smooth I'm not sure we can help you....!

Regarding the black-out; this is precisely what one would expect, given
that each surface filters light of two different primary colours, ie. as
the white light passes through the red surface, it is multiplied by the
pigment (3 * <1, 0, 0> = <3, 0, 0>).  When this filtered light passes
through the blue surface it is multiplied in the same way, and by my
calculations <3, 0, 0> * <0, 0, 1> results in <0, 0, 0>.

To achieve the magenta you are looking for, you need to allow both some
red and blue to filter through both surfaces, eg. using a <3, 3, 3>
light and rgbt <1, .5, .5, 1> and rgbt <.5, .5, 1, 1> pigments, you get
rgb <1.5, .75, 1.5> where the surfaces overlap.

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