Being an NC25, I made a gamble and checked for a corresponding color match on the Temptalia Foundation Matrix for the One Step and my recommended shade was Tone.
The product came in a 1oz bottle with a pump dispenser (similar to the Benefit Stay Don't Stray pump). As per the above photo (taken from the ACW website), the color of the foundation is clearly visible through the see through window on the product label. Before I get into my thoughts on the product in general, here's a blurb from the Stila website:
Press down CTRL and click on above image to enlarge
The One Step Make Up is a revolutionary product that bundles up the functions and benefits of a primer, foundation, concealer and powder into one. It is made up of 100% mineral pigments, paraben free and fragrance free. That said, it should be suitable for pretty much a wide range of skin types. The website claims that the formula has a velvety, mousse-like formula but I'm afraid I beg to differ. Out of the pump, the product has a rather dense texture and is more gel-like than mousse-like. I wouldn't dispense the product directly on the brush bristles (I used a MAC 130 brush for application) due to the texture of the product. I recommend putting some on the back of your hands or a mixing palette and use the brush the pick up the product from there.
The product works quite well in neutralizing redness on my skin and blends easily into skin without streaking. The coverage is definitely buildable and stands true to it's claim of being weightless. The overall finish looked slightly powdery once it dries on the skin but quickly disappears to a smooth finish once set. The formula was neither drying nor oily on my skin and has lasted throughout the day without evident smudging or fading even with frequent touches.
The one con that I've encountered is that it settles into pores and I would highly recommend those with enlarged pores to apply a good primer/filler to those areas before applying this foundation. I noticed (upon closer inspection) that it emphasized my whiteheads (or at least made it appear as if I had white heads where my pores are) as well.
So those are my impressions of the product. I'll have a follow up post with more photos soon. If you have any questions on the product, feel free to leave a comment and I'll either answer you there or in the follow up post.