To minimize vibration and noise, each RCA connector is sealed with an anti micro-phony compound to damp excess vibration in that part of the signal path. This helps to enhance the silent background in your system.
The Black RCA is thought of very highly by people who try it:
“Putting it into my system, I was impressed by just how communicative this modestly priced cable was. Compared to my favourite similarly-priced cable I had to hand TQ offered a significant improvement in focus, timing and overall lucidity.” - Steve Dickinson, HiFi +
“I’d say it sounds one of the very best cables at the price”
David Price, HiFi World 2011