Jon Risch talks about cable jacket colour to some extent on his website. While i don't know if this is actually audible at audio frequencies, i do know that some manufacturers have played with such things at radio frequencies.
In an independent study conducted by a reputable College, identical copper wound heliwhip antennas were made. These heliwhips were then impregnated with fiberglass for rigidity and corrosive purposes. Four different colour dyes were used in the fiberglass: white, orange, black and grey.
When tested, the grey antennas always performed better for some reason. Don't know if the grey dye had better conductivity or less thermal loss, but that's what the tests showed. Never got to see any further results, so i don't know if they were able to find out the reason behind the variations in performance.
As far as twisting vs untwisted, the further that one spaces the cables apart, the more high frequency roll-off will occur. This can tend to soften the treble response of a bright system and / or seem to fill out a somewhat lean sounding system. Twisting the cables will increase the high frequency response of the system by widening the bandwidth of the cabling. This occurs due to reduced inductance.
As far as break-in goes, moving a cable can not only cause stress cracks in the crystal structure of the wire, but may also cause differences in conductivity at the point of termination. This could be either within the connector itself ( wire bonds to connector ) or where the connectors mate externally ( male RCA to female RCA, etc... ).
It is not uncommon for cables to sound slightly different after moving them. After a period of extended signal flow, the sound of the system typically returns to what one was used to. That is, unless the cables were relocated into a different area where they may be exposed to a different ( more OR less ) RFI, EMI, etc... Sean
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