Exemplifies changing the recent apps overview color on Lollipop+ devices.

Notes.txt

1. The text color changes from white to black depending on the color you choose. This isn't controllable.

2. Method params: this.setTaskDescription(new ActivityManager.TaskDescription(String label, Bitmap resource, int Color));

SampleActivity.java

public class SampleActivity extends AppCompatActivity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    //Backward compatibilty; ignored on anything lower than Lollipop
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
      this.setTaskDescription(new ActivityManager.TaskDescription("App Name", // Name 
              drawableToBitmap(getResources().getDrawable(R.mipmap.ic_launcher, null)), // Icon 
              Color.parseColor("#ffffff"))); // Color; this is what you were asking about.
    }
  }
  
  /**
     * Converts a drawable resource into a bitmap
     *
     * @param drawable
     * @return Bitmap
     */
    public static Bitmap drawableToBitmap(Drawable drawable) {
        if (drawable instanceof BitmapDrawable) {
            return ((BitmapDrawable) drawable).getBitmap();
        }

        // We ask for the bounds if they have been set as they would be most
        // correct, then we check we are  > 0
        final int width = !drawable.getBounds().isEmpty() ?
                drawable.getBounds().width() : drawable.getIntrinsicWidth();

        final int height = !drawable.getBounds().isEmpty() ?
                drawable.getBounds().height() : drawable.getIntrinsicHeight();

        // Now we check we are > 0
        final Bitmap bitmap = Bitmap.createBitmap(width <= 0 ? 1 : width, height <= 0 ? 1 : height,
                Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
        drawable.draw(canvas);

        return bitmap;
    }
}