diff --git a/src/vbl_aquarium/models/urchin.py b/src/vbl_aquarium/models/urchin.py
index 04f4480..3094eec 100644
--- a/src/vbl_aquarium/models/urchin.py
+++ b/src/vbl_aquarium/models/urchin.py
@@ -46,7 +46,7 @@ class AtlasModel(VBLBaseModel):
     visible: List[bool]
     colors: List[Color]
     sides: List[int]
-    colormap: str = ''
+    colormap: str = ""
     intensities: List[float] = []
     alphas: List[float]
     materials: List[str]