Hi,
You have sent the wrong second argument to the imadjust. It is either a vector or 2-by-3 matrix, the line below is adjusted you can make the change in the app yourself.
Edit: I made an error. Line in callback of button 3 (low b) should be
app.TempEffect=imadjust(app.Modified,[app.LowR app.LowG app.LowB; app.HighR app.HighG app.HighB]);
