Funny thing: This week, I've been running tests that are very similar to yours,
solely in v3.8 (the latest development version). For my city buildings scene, I
am trying to figure out why two colors-- both evaluated using the eval_pigment()
macro-- return slightly different values, when the values should be identical.

My *current* belief is that the reason has to do with the 'srgb' gamma itself,
as opposed to gamma 2.2. SRGB has a gamma that is not a straight power law (like
2.2), but rather a sort of combination of gammas-- with both a power law segment
and a linear segment. The 'average' of those is not quite 2.2. Wikipedia has a
good article about it. My own results so far show that an SRGB color vs. a
'linear' RGB color (that has been re-transformed into a gamma 2.2 color by using
an inverse power law) produce the slightly different values. AFAIU, the
Wikipedia article gives a rather complex formula which better approximates this
'gamma inversion' of RGB to arrive at the SRGB gamma color, with a better match
between expected values.

I *think* that POV-ray version 3.6 and earlier did not make use of 'srgb' as a
gamma in any way, but rather 1.0 or 2.2, depending on the "user's preference",
ha. I used to use 2.2, but that was because of a basic 'color misunderstanding'
on my part, prior to the introduction of srgb colors. ;-)

I'm still absorbing your comments, and thinking it all through. I need to do a
visual test like yours, in v3.8.

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