fixed it, almost

scam.py

@@ -82,6 +82,7 @@ class MainPanel(wx.Panel):
         self.camera = None
 
         self.orig_cfg = None
+        self.pipeline_cfg = None
 
         self.pls = pls = Pipelines()
 
@@ -160,6 +161,8 @@ class MainPanel(wx.Panel):
         cfg = pipeline.get()
         print("current config:", cfg)
 
+        self.pipeline_cfg = cfg
+
         # use contents of KNOWN_TYPES to pre-fill cfg
         #TODO use setdefault instead?
         cfg_o = cfg
@@ -299,12 +302,16 @@ class MainPanel(wx.Panel):
 
 
     def on_change(self, event):
-        old_cfg = self.orig_cfg
+        old_cfg = self.pipeline_cfg or {}
         new_cfg = self.make_cfg()
 
-        for k, v in KNOWN_TYPES.items():
-            if new_cfg.get(k) is None:
-                new_cfg[k] = v
+        new = {}
+        old = {}
+        for i in sorted(set(old_cfg) & set(new_cfg)):
+            old[i] = old_cfg.get(i)
+            new[i] = new_cfg.get(i)
+        old_cfg = old
+        new_cfg = new
 
         color = wx.Colour(164, 36, 23) if new_cfg != old_cfg else wx.NullColour
         self.btn_save.SetBackgroundColour(color)