You use a zipper to close this bag. Blue is just one of the colours you can pick from if you're going to buy this bag.
From Wardow
Radley London Pockets Crossbody bag dark blue
Freemans
Radley London Pockets Tortoise Large Zip Around Crossbody Bag
Radley
Radley London Women's Leather Leather Pockets Large Zip Around Crossbody - Navy Large