NOAA Hi Def Radar's Display Settings allow for control over multiple visual elements, including the transparency levels of on-screen radar imagery. Under the Layers Menu > Map Options, you can access the display settings and map types. The opacity slider gives you the ability to adjust the level of color intensity and transparency, as seen below. The Map Legend toggle, allows for the legend widget to be toggled on or off.
To see more of the radar map, you can toggle Fullscreen Mode. This allows you to hide the app's toolbar by tapping the expand icon in the left hand corner of the screen. Tapping the icon a second time will return the toolbar to its normal place. If you are using an iPad, the app will also support Landscape Mode when the device is rotated horizontally in addition to Fullscreen Mode.