Thanks to Google Chrome's translator feature, I was able to find a Hungarian website featuring medieval Szeklers heraldry HERE which were put to use below.
I primed horse and rider in the horse's base color with Army Painter colored primer. Then I washed the horse in Devlon Mud and subsequently painted the highlight color onto the horse very neatly, taking care not to slop onto the tack. That way, I could paint the tack in a highlight color and the shadowing from the Devlon Mud remained intact. This is much easier than painting the tack in black and then painting a color over the top of the black. I'll be keeping this trick in my stable!