One means is to go the online Apple Store and go through the process of ordering a new MacBook Air, Choose the model you making sure that you select "Sky Blue" for the color.
On the screen where you can customize the Mac, on the left side is an image of the laptop with its display opened. Directly below that there is a link to "View Gallery." Select that and you can go through the provided images to compare what you have against it.
Alternately, your sales receipt should have the color identified. Lastly, bring your new laptop directly to your local Apple Store and you can compare it against the other model colors.