What color dye is added to 100LL aviation fuel?

The correct answer is blue because 100LL aviation fuel, which is low-lead aviation gasoline used in many piston-engine aircraft, is dyed blue for identification purposes. The blue dye helps to distinguish it from other types of fuel, specifically 100 octane fuel, which is dyed green. This color coding is crucial for ensuring that pilots and ground crew can easily differentiate between fuel types to avoid mixing or using the wrong fuel.

The color blue is a safety measure in the aviation industry, helping to reduce the chance of a dangerous situation where an aircraft might inadvertently be refueled with the incorrect type of fuel that could lead to engine damage or performance issues. The dye colors have established meanings within the aviation community, and adherence to these color codes is important for maintaining safe operational practices.