Grease is made using a base oil, typically mineral oil or vegetable oil, which is what provides the lubrication in grease. Grease works by creating a film between two moving surfaces which is what provides the lubrication (the reduction of friction).
Grease Color and what is means(or doesn’t).
Grease is available in many colors including black, gray, blue, red, purple, yellow, green, and even more colors. The dye colors added to different grades of grease vary from manufacturer to manufacturer. So, for the most part, you cannot rely on the color of grease to determine its suitability for use in any specific application. The one possible exception to this statement is white grease which is normally an indication of a food-grade grease that can be used to lubricate machinery used in the manufacture and processing of food.
typically, gray or black greases contain Molybdenum Disulfide (AKA moly) or Graphite. These additives are put into grease intended for extreme operating conditions such a extremely high pressure rollers or bearings.
Color Change in Grease
Color change in grease over time usually signifes a change in the grease’s performance characteristics. If exposed to high temperatures for long periods of time, a grease can lose intensity of the color in it. A colored grease could change to a black color which may indicate the grease has oxidized and the performance characteristics may have changed. If a grease appears “milky” that could be an indication that it has become contaminated with water which can change the performance characteristics of the grease, and even lead to rusting of the parts in the grease joint.
If any of the above happens to your grease, it likely also is an indication that the grease joint needs to be cleaned and new grease installed to ensure the desired performance characteristics.