A new set of test leads that came with an older model
of Tektronix TekMeter LCD scopemeter consisting of
4 leads, 3 were soft, but the red one was semi-rigid.

Vintage cables are often stiffer after 20-30 years, and
I suppose that's to be expected, but new cables should
be relatively soft.

Perhaps the plasticizer would have unacceptably altered the color.