One of my favorite new features in Inkpad 1.4 is Blend Modes (you can find them under the Shadow and Opacity menu at the bottom of the menu). Blend modes affect the way the color of an object or group is transferred onto the objects below them. By default (Normal Mode), an object is opaque and blocks any objects that may be under it. Using blend modes you can change that. For now lets focus on one particularly useful blend mode – Multiply. I find this mode to be very useful for creating shadows. In the example below I've used Multiply to created the clock shadow and the wallpaper. Notice how the shadow blends into wallpaper.
Try out different Blend Modes and take note how they react with objects. Knowing how to use them may help give your Inkpad drawings the added edge you are looking for.