Okay so I don't smoke or anything but yet my lips are darkish! What is the cause of this?

Pigmented lips. It means that your lips contain your natural color. If concerned, check with your dentist or an oral pathologist to rule out oral pigmented lesions that result from cellular hyperplasia.
Vague. I would see a dr. If this is a daily occurrence. If it is not, then keep a diary when this occurs and note, meds, nutrition, activities, etc.