If your rusticas didn’t turn brown, they were harvested too soon. Since rusticas grow and reach the flowering stage so quickly, most people think that the leaves can be harvested after a couple of weeks after blooming. Wrong. Rusticas should be harvested when the leaves show signs of maturity or, even better, when they begin to ripe (I.e. begin to turn yellow while still on the plant). And this requires a month or more after flowering (and, of course, a lot of patience LOL).
If properly harvested and cured, rustica leaves cure anywhere between copper color to very dark brown, nearly black. This depends on the strain and the ambient humidity, as well as temperature during the cure.
pier