THE DARKNESS IN THE OIL USED IN THE ENGINE REFERS TO?
Dark oil typically means that it has been cycled through your engine too many times and it is time to get it changed.
One of the functions of engine oil is cleaning. A quality engine oil disperses the soot particles formed in the engine and absorbs them, preventing them from sticking to metal surfaces thanks to the additives in its content. It also cleans those that adhere to metal surfaces with detergent.
For this reason, engine oil becomes dirty and darkens in color. Therefore, engine oil that looks dirty means that it is doing its job well.