[android] How can I change the color of AlertDialog title and the color of the line under it

Here is another solution (based on suggested answers) that handles the styling of the dialogs in one class without needing to worry about the state of the dialog when you change the style - dialog can be already shown or just initialized.

Usage example:

AlertDialog.Builder builder = new AlertDialog.Builder(context);
AlertDialog dialog = builder.create(); //or builder.show()
DialogViewDecorator.decorate(dialog, android.R.color.holo_red_light); //can also set the defaut color in the class

Implementation:

public class DialogViewDecorator {

private static final
@ColorRes int DEFAULT_TITLE_DIVIDER_COLOR = android.R.color.holo_orange_light;

public static void decorate(Dialog dialog) {
    decorate(dialog, DEFAULT_TITLE_DIVIDER_COLOR);
}

/**
 * Sets the title divider color when the view is shown by setting DialogInterface.OnShowListener on the dialog.
 * <p/>
 * If you want to do other things onShow be sure to extend OnDecoratedDialogShownListener(call super.show(...)!)
 * and call {@link #decorate(Dialog, int, OnDecoratedDialogShownListener)}.
 *
 * @param dialog
 * @param titleDividerColor
 */
public static void decorate(Dialog dialog, final int titleDividerColor) {
    decorate(dialog, titleDividerColor, new OnDecoratedDialogShownListener(titleDividerColor));
}

/**
 * Method for setting a extended implementation of OnDecoratedDialogShownListener. Don't forget to call super
 * or the titleDividerColor wont be applied!
 *
 * @param dialog
 * @param titleDividerColor
 * @param OnShowListener
 * @param <T>
 */
public static <T extends OnDecoratedDialogShownListener> void decorate(Dialog dialog, int titleDividerColor, T OnShowListener) {
    if (dialog == null || titleDividerColor <= 0) { return; }

    if (dialog.isShowing()) {
        setTitleDividerColor(dialog, titleDividerColor);
    } else {
        dialog.setOnShowListener(OnShowListener);
    }
}

private static void setTitleDividerColor(DialogInterface dialogInterface, int titleDividerColor) {
    try {
        Dialog dialog = (Dialog) dialogInterface;
        int dividerId = dialog.getContext().getResources().getIdentifier("android:id/titleDivider", null, null);
        View divider = dialog.findViewById(dividerId);
        if (divider != null) {
            divider.setBackgroundColor(dialog.getContext().getResources().getColor(titleDividerColor));
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}


public static class OnDecoratedDialogShownListener implements DialogInterface.OnShowListener {
    private int titleDividerColor;

    public OnDecoratedDialogShownListener() {
        this.titleDividerColor = DEFAULT_TITLE_DIVIDER_COLOR;
    }

    public OnDecoratedDialogShownListener(int titleDividerColor) {
        this.titleDividerColor = titleDividerColor;
    }

    @Override
    public void onShow(DialogInterface dialogInterface) {
        setTitleDividerColor(dialogInterface, titleDividerColor);
    }
}}