It's the new Citadel Air paint range: 51 new paints designed to be used with an airbrush and all of them available to pre-order now. Click on this link to see the full range.
The Citadel Air range includes 51 paints, a paint thinner and an airbrush cleaner. The paints are identical in colour (and name) to their Layer or Base counterparts, but specially formulated to be used with an airbrush. This means all you need to do is undercoat your model as normal, load your chosen Air paint into an airbrush and spray away for that perfect basecoat or blended layer. If you make any tiny painting mistakes later on, simply tidy up your work with the Layer or Base paint of the same name. Citadel Air: Steel Legion Drab is the same colour as Citadel Base: Steel Legion Drab, for example. It's that simple.
The Air Caste Thinner can be used to dilute a Citadel Air paint, making the colour more translucent. This is especially handy when you're blending colours over large, flat areas such as tanks or Imperial Knights, enabling you to get a smooth transition between colours by applying several thin layers of your chosen colour rather than one solid one.
The cleaner, meanwhile, is exactly what it sounds like, a cleaner for airbrushes. Designed specifically for cleaning Citadel paints out of nozzles, feeds and hoppers, it's just what you need to keep your airbrush in tip-top condition.
Check out White Dwarf 83 for more information on the Citadel Air range and follow this link to see what colours are available.