Wow, I am surprised I love this product, but I do! This was released with the Summer 2009 collection. I've usually never had good luck with those color-changing lipsticks/glosses. (Remember those mood lipsticks from the 80's?). I find they typically turn a garish shade of pink or fuchsia on me, even the latest incarnations, like Smashbox's O Gloss, or even the Too Faced Smurfette gloss, which I otherwise like.
This looks like one of Dior Addict High Shine lipsticks, in terms of the slant-tip, and the size of the actual bullet. The actual product looks like a translucent baby pink, but once it is applied to the lips, it turns to the perfect "natural" lip color for you by working with your body's natural chemistry. (I think it's something to do with the pH levels in your skin, etc.) For me, it is a mid-tone warm-pink, basically like a rosier version of my natural lip color. The effect is quite natural.
The texture of this is quite balmy and moisturizing, and the finish is like a glossy lipstick. It makes the lips look juicy and healthy. I do find that the color lasts quite long, even after the product is wiped off, but the stain effect is sheer, so you can feel free to apply more without turning your lips a tacky color or risk having the color flake off your lips. It also looks very pretty with the Dior Lip Plumper on top, or a sheer gloss once the sheen of the balm goes away.
Also, this product has SPF 10, which, though it is low, is better than nothing. (Wish they could have done SPF 15 or 30.). I love this stuff, and will be using all of the time. I kind of wish I'd invented it myself! It retails for $28USD (pretty pricey!) -- but is well worth it!