The spectator names their favourite color (or any of the six colors) from the cube. You give them the cube to mix, then take the cube back without looking, and "solve" it behind your back. Actually you don't solve the whole cube, only one side - which has their selected color!
Select "One color only" as the routine, and set the option "Wait after mixing" to either 3sec (when practicing) or to 10-15sec (when performing). Select any of the "Onscreen display" options (audio guide for this routine will be available soon). Then start the routine... Wait till the blue progressbar completes and "Ready to go" or "GO" appears after displaying the name of the routine.
At the beginning of the routine you can ask the spectator what is their favourite color of the six colors on the cube. As you give the cube to them to mix, you secretly turn the side that has the chosen color in the center. So if they choose GREEN, you turn the GREEN side as you ask them to mix the cube (of course you can make more turns before handing them the cube). You will turn around or use a blindfold for the rest of the routine. With each turn they make while mixing, the timer resets so you will have to wait X seconds after the mix before you can proceed with solving the cube.
So when they are ready mixing, they give the cube back behind your back, and you start solving it... The first two moves will always be "Top and right in any direction" or "U R", this way the app will know how you're holding the cube. Then you should follow the steps to solve the cube. If you make a mistake, the app will insert a correction move. If you make too many mistakes in a row, the whole solving process will start over.
When you are ready solving the selected side, you will see "The cube is solved" or a 🙂 smiley on the screen. You then show the cube to the spectator, and they will soon realize you have solved only one side - the one which has their favourite color!