If no identifier is specified then the items modify the finish values in the current default texture. Note that transformations are not allowed inside a finish because finish items cover the entire surface uniformly. The light you see in dark shadowed areas comes from diffuse reflection off of other objects. This light cannot be directly modeled using ray-tracing. However we can use a trick called ambient lighting to simulate the light inside a shadowed area.
Ambient light is light that is scattered everywhere in the room.
It bounces all over the place and manages to light objects up a bit even where no light is directly shining. Computing real ambient light would take far too much time, so we simulate ambient light by adding a small amount of white light to each texture whether or not a light is actually shining on that texture. This means that the portions of a shape that are completely in shadow will still have a little bit of their surface color. It's almost as if the texture glows, though the ambient light in a texture only affects the shape it is used on. Usually a single float value is specified even though the syntax calls for a color.