This outfit took a while. I tried all sorts of various green-themed outfits. Then I tried other colors in all sorts of raiment, and finally this red robe surpassed them all. The bright hue of robe matches the brightness of the green and yellow tack, and the robe, tack, and boots have similar swirls. The white plume of the hat matches the whiteness of the horse, and the gilded brown echoes the leather of the tack.
Head: Plumed Hat (gold)
quest reward for classes that wear light armor (Introduction), no min. level required
Chest: Elven Robe of Might (red)
monster drop, light armor, min. level 30
Hands: Elven Cotton Gloves (gold)
Expert (T3) Tailor recipe, light armor, min. level 22
Feet: Elven Leather Boots of Vigour (red)monster drop, light armor, min. level 30