Welcome to HCM.
You have not mentioned whether you are a male or female.
Most of the time childhood pink colour of the lips gets faded. The pink colour is due to the profuse vascularity of the area and the thinness of the skin covering it. With age the skin becomes thicker and this results in fading of the pink colour. Smoking
also causes the lips to become darker due to increased pigmentation.
If you are female, apply lips stick which is the only remedy available.