The gold colour looks dull because there is no underlying layer of shiny, distortion-causing nickel. So, all you get is clean and pristine audio quality to your speakers. With the colour coded sleeve, it helps identifying speaker wire's polarity in order for your speakers to produce the truest audio frequencies and sound wave from the source.
Dual 2-set screws design will ensure the banana plug stays securely connected to the speaker wires. You may secure both set screws to the bare speaker wires for maximum contact or secure one set screw to the speaker wire's PVC jacket for elasticity strength.