Final answer:
Diesel exhaust fluid (DEF) is associated with the color blue.
Step-by-step explanation:
The color associated with diesel exhaust fluid (DEF) is blue. DEF is a solution of urea and deionized water that is used in selective catalytic reduction (SCR) systems to reduce nitrogen oxide (NOx) emissions in diesel vehicles. The blue color is helpful in visually distinguishing DEF from other fluids in a vehicle.