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

This will set the color for the title, icon, and divider. Bound to change with any new Android version.

java

public static void colorAlertDialogTitle(AlertDialog dialog, int color) {
    int dividerId = dialog.getContext().getResources().getIdentifier("android:id/titleDivider", null, null);
    if (dividerId != 0) {
        View divider = dialog.findViewById(dividerId);
        divider.setBackgroundColor(color);
    }

    int textViewId = dialog.getContext().getResources().getIdentifier("android:id/alertTitle", null, null);
    if (textViewId != 0) {
        TextView tv = (TextView) dialog.findViewById(textViewId);
        tv.setTextColor(color);
    }

    int iconId = dialog.getContext().getResources().getIdentifier("android:id/icon", null, null);
    if (iconId != 0) {
        ImageView icon = (ImageView) dialog.findViewById(iconId);
        icon.setColorFilter(color);
    }
}

Remember to call dialog.show() before calling this method.