There is a condition seen in many cats, especially cats that have any orange or ginger coloring. The spots usually first appear in middle-aged to older cats as small black spots on the lips or nose first. With time, more dots appear and some grow a bit larger.
This condition called lentigo simplex, and it is not a form of cancer. In fact, it is completely harmless, just like human freckles.
There are however, other pigmented skin conditions that can occur anywhere on your pet, including the lips so if you are uncertain, it would be a good idea to have it checked out by your veterinarian. This condition is characterized by small (1mm or less) lesions that may appear close together, discoloring a larger area. The lesions are flat, are not painful or itchy, and do not have any associated redness or other discoloration. If the lesions you are seeing do not fit this criteria, it would be good to have Heaven examined.
I hope this is helpful and if you have any other questions please let me know.