code: @SuppressWarnings("WeakerAccess")
    public SnackbarBuilder appendMessage(@StringRes int messageResId,
                                         @ColorRes int colorResId) {
      return appendMessage(context.getString(messageResId),
          getColor(colorResId));
    }
docs: Add some text to append to the message shown on the Snackbar and a colour to make it.
  
  @param messageResId String resource of the text to append to the Snackbar message.
  @param colorResId   Resource of the colour to make the appended text.
  @return This instance.