diff --git a/sweetbean/const.py b/sweetbean/const.py
index 5c62633..90c106a 100644
--- a/sweetbean/const.py
+++ b/sweetbean/const.py
@@ -81,7 +81,8 @@ def FUNCTION_PREAMBLE(is_async):
     async_string = ""
     if is_async:
         async_string = "async "
-    return f"{async_string}function runExperiment() " + "{\n"
+    return f"{async_string}function runExperiment() " + ("{\n"
+                                                         "document.body.style.backgroundColor = 'black';\n")
 
 
 def FUNCTION_APPENDIX(is_async):