Two ways, either in XAML:
<phone:PhoneApplicationPage.ApplicationBar>
<shell:ApplicationBar BackgroundColor="White" ForegroundColor="Black">
<shell:ApplicationBar.Buttons>
<shell:ApplicationBarIconButton Text="A button" IconUri="/Assets/AppBar/new.png" />
</shell:ApplicationBar.Buttons>
</shell:ApplicationBar>
</phone:PhoneApplicationPage.ApplicationBar>
Or in the code behind:
using System.Windows.Media;
...
ApplicationBar.ForegroundColor = Colors.Black;
ApplicationBar.BackgroundColor = Colors.White;
, BackgroundColor , ForegroundColor . .
opacity, 1 ( ).