Do not use dark and bright lipsticks all the time. Change or alternate light coloured lipsticks also.
If you use dark coloured lipsticks all the time , they'll get you the dark or discoloured lips.
If you have to use lipsticks in the day time, remove them in the night carefully and apply olive oil. Massage olive oil liberally over the lips and leave it overnight if you can. This will get you the softest of lips.
If it has already discoloured, you can apply a mix of glycerine, lime juice and honey, onto your lips. Avoid applying dark lipsticks for sometime. If you have to, then get a good branded one to do so.
Eat plenty of fruits and vegetables. They are good for your health. If the health improves, your skin beauty also improves. That has been proved by many who are in the beauty field.
Drink plenty of water at least 10 glasses and sometimes you may need more. You should always drink water before you feel the thirst. Lips should never get dry.
If you look after all these things and are careful, then you'll have rosy and soft lips forever.