This still mentioned IdlePrefs.py as the place to edit color
preferences. It is now in config.txt or ~/.idle.
diff --git a/Tools/idle/help.txt b/Tools/idle/help.txt
index 001da01..a5d9a73 100644
--- a/Tools/idle/help.txt
+++ b/Tools/idle/help.txt
@@ -104,7 +104,8 @@
The coloring is applied in a background "thread", so you may
occasionally see uncolorized text. To change the color
- scheme, edit the ColorPrefs class in IdlePrefs.py.
+ scheme, edit the [Colors] section in config.txt (or add a
+ [Colors] section to ~/.idle).
Python syntax colors: