We know that both solids and liquids can exhibit metallic luster. I wonder whether there is a gas that when filling a transparent envelope (such as a glass tube) would make it appear with metallic luster?
Good question... would a plasma qualify? Metallic luster is due to a sea of electrons, free to move and to reflect (well, re-radiate) incident radiation. A plasma can be created in a gas, such as the interstellar medium, or in Earth's atmosphere. The Kennelly-Heaviside layer is such a "shiny", reflective layer, causing skip signal propagation to extend the range of radio communication. So if you saw in radio wavelenghts, rather than the visual spectrum, plasma is shiny!
Another possibility would be a Bose-Einstein condensate... but the act of illuminating it tends to destroy it.
Luster is an optical property of minerals, and a mineral is defined as a solid inorganic substance that occurs naturally (that includes metals, of course). The Mineralogic Society of America defines metallic luster (see link) as something that occurs in minerals which have a refractive index greater than 3.
I wasn't able to find any gases with a refractive index even close to the cutoff value. I'd say the answer is no, and that what might appear to be luster is instead scattering of incident light (not refraction).
Not an answer to your question ... but This may interest you! (Or your curiosity)
As for your question : I guess not! The colours of gases are caused by selective absorption of light so that the light coming through the gas is coloured - it is not light reflected from the gas.
Reflection occurs when light passes from an optically dense medium to an optically less dense medium, or vice versa. In other words, there has to be a change in the optical properties of a gas to cause reflection. The gas molecules individually are to small to significantly effect the photons of light.