Final answer:
An oxygen tank containing 100% O2 is typically green in color to indicate that it contains oxygen, which is highly flammable.
Step-by-step explanation:
An oxygen tank containing 100% O2 is typically green in color.
Oxygen itself is a colorless gas, but oxygen tanks are often painted green to distinguish them from other gas cylinders and to indicate that they contain oxygen. This is done for safety reasons, as oxygen supports combustion and is highly flammable.