I was interested in getting "colors" too. But I decided I'm going to pass all of my colorful nylon stuff down and get a leather breast collar and headstall and I am going to get a neutral wool saddle pad. Then for "colors' I will just have my reins and my boots/polos which are normally replaced after a period of time, and reins are cheap, so I can change my color whenever I want. You don't want to be limited to colors because you will find a really good deal on something and won't want to get it because it doesn't match.
But If you still want colors, I would say it's more of a preference of what your favorite colors. But I think Purple or Lime Green would look best.
"If your horse says no, you either asked the wrong question, or asked the question wrong."