Greens and Browns Backyard Composting is primarily a biological process so you must feed your microorganisms to keep them happy. For example, coffee grounds are a nitrogen source. They are generally brownish or darker in color. Browns decompose at low temperatures unless combined with a source of nitrogen. Finding a mix of greens and browns that is in balance can be important.
Carbon is the energy source for the microbes that help break down the materials.
The most conservative response to these concerns is to avoid adding these materials to the composting system. However, many people who compost at home use their own judgement about what materials can be added to the compost system.