Before a late-model vehicle’s engine oil change, a technician may notice that the engine oil has a yellow-green or orange tint that could be mistaken for crankcase contamination.

This coloration may be due to engine oil dye that is added at the assembly plant during engine hot testing and does not alter the lubrication quality of the engine oil.

If in doubt, a black light may be used to determine if dye is in the oil.

Source: Auto Service Professional