--- a/hgext3rd/topic/__init__.py	Fri Aug 26 12:37:52 2016 +0200
+++ b/hgext3rd/topic/__init__.py	Fri Aug 26 12:52:06 2016 +0200
@@ -50,6 +50,7 @@
               'topic.list.behindcount': 'cyan',
               'topic.list.behinderror': 'red',
               'topic.stack.index': 'yellow',
+              'topic.stack.index.base': 'none dim',
               'topic.stack.state.base': 'dim',
               'topic.stack.state.clean': 'green',
               'topic.stack.index.current': 'cyan',       # random pick

--- a/hgext3rd/topic/stack.py	Fri Aug 26 12:37:52 2016 +0200
+++ b/hgext3rd/topic/stack.py	Fri Aug 26 12:52:06 2016 +0200
@@ -18,19 +18,21 @@
     fm = ui.formatter('topicstack', opts)
     prev = None
     entries = []
+    idxmap = {}
     for idx, r in enumerate(getstack(repo, topic), 1):
         ctx = repo[r]
         p1 = ctx.p1()
         if p1.obsolete():
             p1 = repo[_singlesuccessor(repo, p1)]
         if p1.rev() != prev and p1.node() != node.nullid:
-            entries.append((None, p1))
-        entries.append((idx, ctx))
+            entries.append((idxmap.get(p1.rev()), False, p1))
+        entries.append((idx, True, ctx))
+        idxmap[ctx.rev()] = idx
         prev = r
 
     # super crude initial version
-    for idx, ctx in entries[::-1]:
-        if idx is None:
+    for idx, isentry, ctx in entries[::-1]:
+        if not isentry:
             symbol = '^'
             state = 'base'
         elif repo.revs('%d and parents()', ctx.rev()):
@@ -43,6 +45,7 @@
             symbol = ':'
             state = 'clean'
         fm.startitem()
+        fm.data(isentry=isentry)
         if idx is None:
             fm.plain('  ')
         else:

--- a/tests/test-topic-stack.t	Fri Aug 26 12:37:52 2016 +0200
+++ b/tests/test-topic-stack.t	Fri Aug 26 12:52:06 2016 +0200
@@ -194,7 +194,7 @@
   $ hg top -l
   t6: c_f
   t5: c_e
-    ^ c_d
+  t2^ c_d (base)
   t4@ c_h (current)
   t3: c_g
   t2: c_d
@@ -236,7 +236,7 @@
   $ hg topic --list
   t6$ c_f (unstable)
   t5$ c_e (unstable)
-    ^ c_D
+  t2^ c_D (base)
   t4: c_h
   t3: c_g
   t2@ c_D (current)