Nitrogen - N2
Nitrogen is a colorless and surprisingly inert gas. Displaying the gas itself in an interesting way is very difficult. When a current flows through the gas at low pressure, however, an intense and brightly colored light is emitted. It is hard to capture the precise color with a digital camera. The color is pink, with a bluish hue. There is, however, a lot of UV-light, which gives a strong blue color, when kept near paper or other white surfaces. The digital camera also captures this light as blue color.
The picture above shows a tube, filled with nitrogen at low pressure, of approximately 20 cm length, which is connected to a 3300 V AC source, in series with a 400 kΩ resistor in order to limit the current. An UV-filter was used to limit UV-light, entering the camera, but not all of the UV light can be kept away from the camera and this may result in too much of a bluish hue.