This transparent what you see is what you get is a warm brown, meaning it has tint of reddish amber to lighten up the color.  Sienna is a cinnamon brown that can be predictable and the intensity can be controlled by thickness of color application.  When drawing down into stringers you can encase solid clear or color with Sienna and achieve a very light tint, or in blown application get an extremely subtle tint by sandwiching in clear and blowing thin. 

Sienna handles just like Glass Alchemy Beryl or Glass Alchemy Cobalt 1, in the way that is holds heat well, melts into itself smoothly, and leaves no trace of where color was layered upon itself.  Great for blow in or puff and stuff maneuvers when you need a tube of consistent color tone to work with.