I will add my answer since I don't use any of the other answers provided.
With the Support Library v7, all the styles are actually already defined and ready to use, for the standard buttons, all of these styles are available:
style="@style/Widget.AppCompat.Button"
style="@style/Widget.AppCompat.Button.Colored"
style="@style/Widget.AppCompat.Button.Borderless"
style="@style/Widget.AppCompat.Button.Borderless.Colored"
Widget.AppCompat.Button: 
Widget.AppCompat.Button.Colored: 
Widget.AppCompat.Button.Borderless 
Widget.AppCompat.Button.Borderless.Colored: 
To answer the question, the style to use is therefore style="@style/Widget.AppCompat.Button.Colored".
How to change the color
For the whole app:
The color of all the UI controls (not only buttons, but also floating action buttons, checkboxes etc.) is managed by the attribute colorAccent as explained here. You can modify this style and apply your own color in your theme definition:
<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
...
<item name="colorAccent">@color/Orange</item>
</style>
For a specific button:
If you need to change the style of a specific button, you can define a new style, inheriting one of the parent styles described above. In the example below I just changed the background and font colors:
<style name="AppTheme.Button" parent="Widget.AppCompat.Button.Colored">
<item name="colorButtonNormal">@color/Red</item>
<item name="android:textColor">@color/White</item>
</style>
Then you just need to apply this new style on the button with:
android:theme="@style/AppTheme.Button"