Update app.py

app.py

@@ -20,6 +20,7 @@ from detectron2 import model_zoo
 from detectron2.engine import DefaultPredictor
 from detectron2.config import get_cfg
 from detectron2.utils.visualizer import Visualizer
+from detectron2.utils.visualizer import ColorMode
 from detectron2.data import MetadataCatalog, DatasetCatalog
 from detectron2.checkpoint import DetectionCheckpointer