As I replied in another comment: > Oil changes color as it captures contaminates such as soot, carbon deposits, etc. It can operate effectively while brown-ish

As I replied in another comment: > Oil changes color as it captures contaminates such as soot, carbon deposits, etc. It can operate effectively while brown-ish, but if the oil is carrying too much it will blacken and start to thicken at which point it will be much less effective at lubricating your engine.