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100LL aviation gasoline has what color when properly grade-coded?

Choices

Clear or straw.
Clear/straw is jet fuel (Jet A) — using it in piston engine causes failure.
✓ Blue.correct
100LL (Low Lead) is dyed BLUE. Other grades: 80 was red (largely phased out), 100 was green, jet fuel is clear/straw. A pilot drawing a sample expecting blue who sees clear or another color should investigate immediately — wrong fuel grade can damage the engine.
Green.
Green was 100 octane (mostly phased out), not 100LL.
Red.
Red was 80 octane (phased out).

Why

100LL (Low Lead) is dyed BLUE. Other grades: 80 was red (largely phased out), 100 was green, jet fuel is clear/straw. A pilot drawing a sample expecting blue who sees clear or another color should investigate immediately — wrong fuel grade can damage the engine.

FAA source: FAA-H-8083-25C, PHAK Ch. 7, fuel systems / aviation fuel grades and colorsbrowse the reference library →

Covered in Supplemental · II — Preflight Procedures — study the lessons free, then practice with grading and mastery tracking.

Original study question written for this course — representative of FAA knowledge-test topics, not an actual current FAA exam question.