Tertiary colors need to return for armor. Would make the tiny differences in armor skins more noticeable.
I liked how Halo 2 used your primary color as a secondary color in team games. I was always disappointed that none of the future games kept that.
I miss having your emblem on your armor as well. It'll never happen in H5, but I'd really like the option to choose where your emblem is placed, like on your back, or shoulder, or the little chest spot like in Reach. Being able to drag the decal around wherever you want and resize/rotate it would be amazing.