According to traditional Chinese medicine your mouth and lips belong to the earth element, to the Spleen and Stomach (this also includes the digestive organs such as the intestines).
What do you see when you look at your mouth in the mirror?
The color of the lips corresponds to blood flow and energy in the digestive organs as well as the expression of moods.
Pink, red pale lips:
Normal lips are pink or pale red in color, a sign of strength in the Spleen. This shows an even temperament. People with these lips can express themselves if they want to and hold back if they prefer. They can manage their moods and usually maintain consistency in mood.
If the color of the lips is pale, it is a sign of lack of blood flow and a lack of energy in the Spleen (Qi or Blood deficiency), or coldness, which creates mild sensitivity. Probably your digestion is weak especially with a blood deficiency, think of crying and feeling insulted quickly.
Very red lips:
Redness indicates heat. The affected organ is often the stomach. There is fire trapped in the Spleen and heat in the Stomach. The Spleen is overactive, and the person possessing this trait is usually very moody, think of someone being explosive, feeling anger quickly.
Dry, cracked lips:
Heat and dryness in the Stomach. There can also be other indicators for dryness and/or heat in the body like dry hands and feet, dry mucus in the nose.
Red and swollen gums: indicate Stomach fire.
Bleeding gums: red and swollen states say that the fire of the stomach damages the blood vessels.
To give you a few other examples of what you can read from the mouth and lips:
Swollen under lip: too much damp, mostly in the intestines
Excessive salivation: too much damp
Tendency towards cold sores: damp heat
Blue, violet lips: cold or pain
Cracked mouth corners: could indicate a yeast infection