I have a small nit-pick about the in-built documentation at "2.3.5.1 Pigments"
within the first paragraph. (It's also in the online wiki, in "Tutorial Section
3.3", under "Advanced Texture Options / Pigments"...

http://wiki.povray.org/content/Documentation:Tutorial_Section_3.3#Gamma_in_Legacy_Scenes

Both places say this:
"Pigments can also be layered one on top of the next so long as the uppermost
layers are at least partially transparent so the ones beneath can show through."

As this is mentioned as a 'general' statement in the very first paragraph, and
before any qualifications are given, a naive or new-user might naturally assume
that the following construct is a nice way to get, for example,  a sort of
color-filtered bozo effect.(I'm using specific pigments to clarify the point)...

texture{
pigment{bozo}
pigment {rgbt <.2,.5,.7,.5>
......

But that doesn't work-- the second pigment completely overrides the first, which
could be a frustrating surprise-- because adding pigments together this way is
not what is really meant by the doc's initial description *as it stands*. (Only
later in the docs is the pigment_map introduced, and/or multiple textures, which
are the correct methods of using/overlaying multiple pigments.) BTW, I was
tripped up by this too, when I first started using POV-Ray.

I would suggest a simple addition to the end of the documentation's sentence,
maybe in parentheses: "See "Using Transparent Pigments and Layered Textures"
below."  That should remove any mystery.

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