Be careful about using colour-fading as a guide to the performance of rope
in sunlight - the differences tell you more about the pigment used than the
UV resistance of the rope itself. Anything coloured red will fade quickly.
Blue pigment takes longer to fade. The pigment most resistant to UV is
Black also is by far the best pigment to prevent the UV from affecting the
underlying structure, and white is the worst. This means that, regardless of
the intrinsic UV-resistance of the basic material, almost ANYTHING which is
loaded with a black pigment, or is painted black, will be highly resistant
to UV. On the other hand, if you really want it white or a light colour,
then you may need to go into more detail to discover what the basic material
is made of.
My antenna came down the other day in a high wind, but it was quite clear
that it had suffered UV degradation over 11 years. It was a white
polypropylene rope with a white polycarbonate jacket (sold as washing line!)
but the jacket had almost completely broken up and the UV had attacked the
inner rope. I replaced it with more of the same because I still had some
left from when I first put it up. I don't know if you can get black
polypropylene but that's what I would recommend you try to find.