undo saving color if text not exist yet. raise error telling user the order to call the functions.

Author: FoamyGuy

adafruit_matrixportal/matrixportal.py

@@ -254,10 +254,12 @@ def set_text_color(self, color, index=0):
         :param index: Defaults to 0.
 
         """
-        self._text_color[index] = color
         if self._text[index]:
             color = self.html_color_convert(color)
+            self._text_color[index] = color
             self._text[index].color = color
+        else:
+            raise IndexError(f"index {index} is out of bounds. Please call add_text() and set_text() first.")
 
     def set_text(self, val, index=0):
         """Display text, with indexing into our list of text boxes.