bottled gas

Gas supplied under pressure in metal cylinders. The term includes pressurized gas (e.g. oxygen and nitrogen cylinders) and gases liquefied under pressure (e.g. liquid butane for use as a fuel). Color conventions are used to identify the type of gas or, in some cases, the specific gas. The color indicating the contents is that of the shoulder of the cylinder at the top. The convention is not international, and practice differs in different countries. In the UK, the convention is:
Yellow for toxic or corrosive gases
Red for flammable gases
Light blue for oxidizing gases
Maroon for acetylene
Dark green for argon
Grey for carbon dioxide
Brown for helium
Blue for nitrous oxide
Black for nitrogen
White for oxygen