Recommendation for an audiophile speaker cord that is not "bright"?

Not helpful perhaps but Wilsons can sound bright if your ears are sensitive to those frequencies (mine are and I can’t tolerate Wilsons). I do not think speaker cable can overcome this. 

Triode Audio labs they are consistant at many shows .I personally have owned top name cables at several times there cost 
and here are as good and better in most cases .
and I own there American series digital and high power cords $5-700 they are a true bargain using only top Copper connectors not cheap gold over brass like most. To enhance and protect your 
connectors stabilant -22 is great including vacuum tube pins 
first clean all connectors with pure isopropyl alcohol .
for AC connectors Furutech nano fluid,it  is excellent but takes 2-3 weeks to dry but for sure enhances detail . Just a tip .

Elsdon Wonfor audio LS25.  These are a proprietary alloy  they are utterly transparent with no phase distortions. If you have a well balanced high end system that you like,  these will give you what you have in spades. Pinpoint stereo imaging , WIDE soundstage true speaker response.

The designer was responsible for tellerium Q cable designs but parted company and took forward some of their design principles.  

As the OP, just saying that I loved the sound of my system before I tried the Nordost Frey 2, Valhalla 1 or Valhalla 2 speaker cables.

I have Nordost Valhalla power cords, Nordost QBase and a dedicated main and ground, and a Nordost QPoint under my preamplifier. These were tremendous, incremental upgrades that really "lowered the noise floor." 

So, I love my Wilson speakers and the rest of my system.

I realize I will probably get a lot of heat for saying this but it’s Christmas time so what the hell. The primary reasons cables sound bright can be placed right at the doorsteps of (1) they aren’t broken in yet, (2) they’re in the wrong direction and (3) it’s something else in the system that’s producing bright sound.