Used as a blue dye in automotive and industrial lubricants, fuels, and petroleum products to aid in leak detection, system tracing, and grade or type identification. Commonly added to refrigeration compressor oils, air conditioning systems, diesel, and gasoline to identify fluid circulation, locate leaks, and distinguish low-tax or tax-exempt grades to prevent misuse (e.g., agricultural diesel in road vehicles). Also applied in specialty inks and dyes for marking purposes where visible tracking of fluid movement is required. Its high solubility in non-polar solvents makes it suitable for use in hydrocarbon-based formulations.