When a photoshop document is uploaded with Craft Sync and a layer is set to transparent inside of an artboard with a background color set to white, the background of your design may appear white. If you want to change the background of your artboard to transparent, follow these instructions:
Click the artboard.
Go to the Properties panel (Window > Properties) for the artboard.
Under artboard background color, select the background and change it to transparent.
Re-sync your artboard using Craft Sync and your background should now display transparency.