Oh my. What a fascinating thread. Haven't read all the responses yet, but I've been mulling this one over. I think your question goes straight to the heart of a lot of what we all try to do with self-presentation.
I'll say straight out that I got 99 problems but body image ain't one. In general, I'm fairly comfortable with my appearance. I don't consider myself a great beauty but I do feel lucky to have been blessed with the raw materials to wear bold colours and avant-garde silhouettes. But there are many other aspects of my self-image which contribute to the way I present myself.
Here's the thing. I went to school with a bunch of rich kids, which meant that clothes were very important. Unlike many of them, I didn't have much money to spend on clothes, but I learned to sew in my early teens and found that wearing cool stuff that nobody else had generated a bit of kudos. Not much, but enough to get by. Clothes were my armour and fashion became crucial to reinforcing my self-image at a fairly young age. I can't say that's changed much, and as I've grown older my confidence has grown and with it my willingness to experiment. It's part and parcel of who I am.
With regard to make-up, I don't wear much of it. My problem skin and irritable eyes are both best left alone. I don't use much more than SP15 mattifying moisturiser and micropowder. But lippy? That's an essential in my book, along with dyed hair and eyewear. I'm much happier when I feel coloured in.
Angie, lisap and others make a good point about make-up being essential in some places for a polished, professional look, while rachylou rightly points out that other cultures favour a natural look. Around here, it's neither here nor there. Some ladies do, some don't, nobody's going to make explicit assumptions and so I'm happy to have the choice.
Circling back to self-image, we hack our appearance for all sorts of reasons. For me, some of those hacks are vital to how I feel about myself. For instance, I rarely go without lipstick and I hate leaving the house in an ill-conceived outfit. Some people might look at me and think I'm brave to dress the way I do, but in fact this is the armour and I don't feel safe without it.
So to answer your question, no, I've never needed a positive self-image to wear a bright lip, but it went a long way to helping me create one.