No, the Infinity Jacket does not feature a two-way zipper.
As you can see in specs, the Neutrino Endurance uses 7 oz of 800-fill down while the Infinity uses 6.3 oz of 850-fill down. The Neutrino Endurance as a while also weighs 5.3 oz more than the Infinity. In addition, as you can see by the image, the baffling in the Infinity has much more stitched through seams than the Neutrino Endurance. Each seam is a potential cold spot. Therefore, the Neutrino endurance is most likely going to be the warmer coat.
We do not stock the Dark Shark XS size online, but if you will contact our customer service by email or phone they can special order that size for you.
Ink is a teal blue-like color. We'll update our data soon, but in the meantime you can view it here: http://us.rab.uk.com/products/womens-clothing/down_2/women-s-infinity-jacket.html
UK S M L XL (compare all sizing chart to the UK sizing)
US S M L XL
EU 46 50 54 58
JPN M L XL XXL