Modern GG "stainless" track is just that - stainless steel, all 3 rails, center rail not blackened, mounted in UV-resistant plastic ties. The stainless rail is far less shiny (and therefore better-looking) than the chrome-y tinplated rail.
Never put wooden-tie track outside. Ever. The wood is pretty lightweight anyway, and - unless you live in the dry Southwest - it should never leave the comfort of a building. And even in Phoenix, not often.
Some people confuse "stainless" with "plated" track. Tin plating resists rust and can easily take solder, but it isn't stainless steel (which is essentially rust-proof, to my understanding) and isn't for outside use. Tin is an expensive metal used to coat steel.
