What grade of fuel is colored blue?

The correct answer pertains to aviation fuel commonly used in piston aircraft engines. The grade of fuel that is colored blue is 100LL, which stands for "100 Low Lead." This type of fuel is specifically formulated for aviation use and has a color code indicating its specific properties.

The "LL" in 100LL signifies that it contains lower amounts of lead compared to older aviation fuels, which is crucial for modern aircraft engines designed to operate more efficiently and with less environmental impact. The blue color helps with easy identification, distinguishing it from other grades, particularly for safety reasons, as pilots must ensure they are using the correct fuel type for their aircraft.

In contrast, the other options refer to different grades of aviation fuel that do not match the blue color designation. For instance, avgas 100 is often associated with green, while 80 octane fuel has a different application and is typically colored differently. Thus, 100LL is specifically recognized for its blue color and its significance in aviation fuel types.