I played around a bit with your settings. And yes, your observation is correct,
but the interpretation is wrong. In fact the texture /* is */ rotated with the
object. Unfortunatelly it doesn't looks so. Even not correct in this case,
Thomas's assumption of a crand-pattern was a valuable hint to trace the
phenomenon down to animation isuues.

An interesting issue one will not notice, if one doesn't work with animations
much. As you can see the texture becomes more and more stable the higher the
texture is scaled.

I used the rust texture supplied by Janc and changed only the scale from his 0.1
at the start to 2 at the end of the animation.

I don't know how POV choosed the colors at a pixel finally (most likely I will
earn a link to the POV Wiki with that confession;-), but independent of the
algorithm, it takes a choice out of a lot of possible colors. The finer the
texture the more colors are at competition. One (or the mean or whatever) wins.
By rotating the structure every point at the structure comes to an  other pixel
and every pixel has a new collection of colors to choose only one from. With a
very heterogenous texture like Janc's rust, one observes an effect like crand
produces in an animation. If the texture becomes more homogenous (here with a
higher scale) the phenomenon becomes less visible while still present.

So my recommendation is to use a higher scaling factor and play a bit more with
the thresholds within the color_map.

I apologise in advance: I have not much experience with animations and I'm only
able to produce mpeg1-files with ffmpeg. Most likely you have to download the
file to your harddrive and watch it from there :(

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