Fix the background color bug when exporting video with the "random" b…

…ackground option (nerfstudio-project#2831)

patch nerfstudio-project#2815

nerfstudio/models/splatfacto.py

@@ -222,7 +222,9 @@ def populate_modules(self):
 
         self.crop_box: Optional[OrientedBox] = None
         if self.config.background_color == "random":
-            self.background_color = torch.rand(3)
+            self.background_color = torch.tensor(
+                [0.1490, 0.1647, 0.2157]
+            )  # This color is the same as the default background color in Viser. This would only affect the background color when rendering.
         else:
             self.background_color = get_color(self.config.background_color)