Youre probably too young to have a scar tissue or callous skin patch deep under the lip, does the skin on the white prt feel thicker or toughter than the rst of the lip?
also, I'd guess youd have to have had a LOt of fever blisters to turn that much of your lip color. I had them growing up too, they are said to be viral and hereditary, and it is aggravatred be various things, for me too much sun, post stress, or too much acid. i have not had any in awhile, and the last one i had ran a shorter course to healing than the previous ones. I chalk it up to cleansing and a much improved quality of diet being the reason it was not a painful, bigger, or long lasting as previous ones. In general fever blisters erupted for me due to toxins if you think about what I think caused them, too much of this or that.

Anyway, in regard to your lip, you cant go wrong with better diet and living practices. Sometimes (most times) it doesnt matter what caused it, only what to do to cure it, and better diet and living practices, practical steps as discused on curezone can only help, and maybe in time you will link the white color to it's cure, if not ever the cause.