Blues in the autumn strike a different mood from that of  the traditional expectation of reds and golds of the fall. And yet, there are many blues in the autumnal palette. The very blue perennial ageratum, or mistflower have tumbled in the heat to embrace the dahlias. Some may call it a shade of lavender, but I consider my Russian sage a part of my autumnal blues. If I allow lavender Russian sage I will also allow purple…