Fix f-string in color error message (#8639)

torchvision/utils.py

@@ -604,9 +604,9 @@ def _parse_colors(
                 f"Number of colors must be equal or larger than the number of objects, but got {len(colors)} < {num_objects}."
             )
     elif not isinstance(colors, (tuple, str)):
-        raise ValueError("`colors` must be a tuple or a string, or a list thereof, but got {colors}.")
+        raise ValueError(f"`colors` must be a tuple or a string, or a list thereof, but got {colors}.")
     elif isinstance(colors, tuple) and len(colors) != 3:
-        raise ValueError("If passed as tuple, colors should be an RGB triplet, but got {colors}.")
+        raise ValueError(f"If passed as tuple, colors should be an RGB triplet, but got {colors}.")
     else:  # colors specifies a single color for all objects
         colors = [colors] * num_objects