diff -r 13bbcd56c57a -r c4e8fa2b1c40 mercurial/debugcommands.py
--- a/mercurial/debugcommands.py	Tue Feb 28 11:13:25 2017 -0800
+++ b/mercurial/debugcommands.py	Tue Feb 21 18:41:37 2017 +0100
@@ -31,6 +31,7 @@
     bundle2,
     changegroup,
     cmdutil,
+    color,
     commands,
     context,
     dagparser,
@@ -344,6 +345,51 @@
         error = _(".hg/dirstate inconsistent with current parent's manifest")
         raise error.Abort(error)
 
+@command('debugcolor',
+        [('', 'style', None, _('show all configured styles'))],
+        'hg debugcolor')
+def debugcolor(ui, repo, **opts):
+    """show available color, effects or style"""
+    ui.write(('color mode: %s\n') % ui._colormode)
+    if opts.get('style'):
+        return _debugdisplaystyle(ui)
+    else:
+        return _debugdisplaycolor(ui)
+
+def _debugdisplaycolor(ui):
+    oldstyle = ui._styles.copy()
+    try:
+        ui._styles.clear()
+        for effect in color._effects.keys():
+            ui._styles[effect] = effect
+        if ui._terminfoparams:
+            for k, v in ui.configitems('color'):
+                if k.startswith('color.'):
+                    ui._styles[k] = k[6:]
+                elif k.startswith('terminfo.'):
+                    ui._styles[k] = k[9:]
+        ui.write(_('available colors:\n'))
+        # sort label with a '_' after the other to group '_background' entry.
+        items = sorted(ui._styles.items(),
+                       key=lambda i: ('_' in i[0], i[0], i[1]))
+        for colorname, label in items:
+            ui.write(('%s\n') % colorname, label=label)
+    finally:
+        ui._styles.clear()
+        ui._styles.update(oldstyle)
+
+def _debugdisplaystyle(ui):
+    ui.write(_('available style:\n'))
+    width = max(len(s) for s in ui._styles)
+    for label, effects in sorted(ui._styles.items()):
+        ui.write('%s' % label, label=label)
+        if effects:
+            # 50
+            ui.write(': ')
+            ui.write(' ' * (max(0, width - len(label))))
+            ui.write(', '.join(ui.label(e, e) for e in effects.split()))
+        ui.write('\n')
+
 @command('debugcommands', [], _('[COMMAND]'), norepo=True)
 def debugcommands(ui, cmd='', *args):
     """list all available commands and options"""