LOL! That pic looks like the horse has the cat by the tail!
I had two sorrel horses and I used regular chestnut oil colored tack on them...black didn't look good, the light stuff looked too much like the color of human skin when up against them - but the regular chestnut oil (which was the same color as my horses) actually turned out best. Contrast with a different saddle pad color (dark green, navy, dark country reds, earth tones, dark browns) to make your tack pop. That's what I did anyway...!! Does this help maybe? Hobby Horse Clothing Co. - Shopping
I know it is mostly for clothes, but it rings true for tack color as well.