The bad news
Like BoD says, it's meaningless to tint a Button's background in Lollipop 5.0 (API level 21).
The good news
Lollipop 5.1 (API level 22) seems to have fixed this by changing btn_mtrl_default_shape.xml (among other files): https://android.googlesource.com/platform/frameworks/base/+/6dfa60f33ca6018959ebff1efde82db7d2aed1e3%5E!/#F0
The great news
The new support library (version 22.1+) adds backward-compatible tinting support to lots of components, including AppCompatButton!
Unfortunately, the android:backgroundTint property still doesn't work (maybe I'm doing something wrong) -- so you have to set the ColorStateList in code, using setSupportBackgroundTintList(). It'd be really nice to see android:backgroundTint supported in the future. Update: Marcio Granzotto commented that app:backgroundTint works on AppCompatButton! Note that it's app:, not android:, because it's in the app/library.
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<AppCompatButton
android:id="@+id/mybutton"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:text="Testing, testing"
app:backgroundTint="#ff00ff"/>
</LinearLayout>
Your activity will automatically inflate an AppCompatButton instead of the normal Button if you let it inherit from AppCompatActivity.
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
AppCompatButton v = (AppCompatButton) findViewById(R.id.mybutton);
ColorStateList csl = new ColorStateList(new int[][]{new int[0]}, new int[]{0xffffcc00});
v.setSupportBackgroundTintList(csl);
}
}
You should of course get the ColorStateList from a color resource, but I was lazy, so...
Oh, and don't forget to base your app theme on one of the Theme.AppCompat themes, or the compat views will be very, very sad... ;)
This worked on both 2.3.7 (Gingerbread MR1) and 5.0 (Lollipop 'Classic').