Murkiness in the tea occurs when tannins, the compounds that give the tea a bitter flavor, and caffeine, which is present in most teas, clump together.
To prevent these chemicals from binding, allow your tea to cool to room temperature, which takes at least one hour, before refrigerating it or adding ice.
Brewing tea at hot temperatures can also cloud it, so a cold brew is a good option for crystal-clear tea. If your tea is already cloudy, a pinch of baking soda will clear it up.