color: reflect the new default in global help topic

We point out that color is enabled by default.

mercurial/help/color.txt

@@ -1,134 +1,139 b''
-Mercurial can colorizes output from several commands.
+Mercurial colorizes output from several commands.
 
 For example, the diff command shows additions in green and deletions
 in red, while the status command shows modified files in magenta. Many
 other commands have analogous colors. It is possible to customize
 these colors.
 
-To enable color use::
+To enable color (default) use::
 
   [ui]
   color = auto
 
+To disable color use::
+
+  [ui]
+  color = never
+
 Mode
 ====
 
 Mercurial can use various system to display color. The supported modes are
 ``ansi``, ``win32``, and ``terminfo``.  See :hg:`help config.color` for details
 about how to control the mode
 
 Effects
 =======
 
 Other effects in addition to color, like bold and underlined text, are
 also available. By default, the terminfo database is used to find the
 terminal codes used to change color and effect.  If terminfo is not
 available, then effects are rendered with the ECMA-48 SGR control
 function (aka ANSI escape codes).
 
 The available effects in terminfo mode are 'blink', 'bold', 'dim',
 'inverse', 'invisible', 'italic', 'standout', and 'underline'; in
 ECMA-48 mode, the options are 'bold', 'inverse', 'italic', and
 'underline'.  How each is rendered depends on the terminal emulator.
 Some may not be available for a given terminal type, and will be
 silently ignored.
 
 If the terminfo entry for your terminal is missing codes for an effect
 or has the wrong codes, you can add or override those codes in your
 configuration::
 
   [color]
   terminfo.dim = \E[2m
 
 where '\E' is substituted with an escape character.
 
 Labels
 ======
 
 Text receives color effects depending on the labels that it has. Many
 default Mercurial commands emit labelled text. You can also define
 your own labels in templates using the label function, see :hg:`help
 templates`. A single portion of text may have more than one label. In
 that case, effects given to the last label will override any other
 effects. This includes the special "none" effect, which nullifies
 other effects.
 
 Labels are normally invisible. In order to see these labels and their
 position in the text, use the global --color=debug option. The same
 anchor text may be associated to multiple labels, e.g.
 
   [log.changeset changeset.secret|changeset:   22611:6f0a53c8f587]
 
 The following are the default effects for some default labels. Default
 effects may be overridden from your configuration file::
 
   [color]
   status.modified = blue bold underline red_background
   status.added = green bold
   status.removed = red bold blue_background
   status.deleted = cyan bold underline
   status.unknown = magenta bold underline
   status.ignored = black bold
 
   # 'none' turns off all effects
   status.clean = none
   status.copied = none
 
   qseries.applied = blue bold underline
   qseries.unapplied = black bold
   qseries.missing = red bold
 
   diff.diffline = bold
   diff.extended = cyan bold
   diff.file_a = red bold
   diff.file_b = green bold
   diff.hunk = magenta
   diff.deleted = red
   diff.inserted = green
   diff.changed = white
   diff.tab =
   diff.trailingwhitespace = bold red_background
 
   # Blank so it inherits the style of the surrounding label
   changeset.public =
   changeset.draft =
   changeset.secret =
 
   resolve.unresolved = red bold
   resolve.resolved = green bold
 
   bookmarks.active = green
 
   branches.active = none
   branches.closed = black bold
   branches.current = green
   branches.inactive = none
 
   tags.normal = green
   tags.local = black bold
 
   rebase.rebased = blue
   rebase.remaining = red bold
 
   shelve.age = cyan
   shelve.newest = green bold
   shelve.name = blue bold
 
   histedit.remaining = red bold
 
 Custom colors
 =============
 
 Because there are only eight standard colors, Mercurial allows you
 to define color names for other color slots which might be available
 for your terminal type, assuming terminfo mode.  For instance::
 
   color.brightblue = 12
   color.pink = 207
   color.orange = 202
 
 to set 'brightblue' to color slot 12 (useful for 16 color terminals
 that have brighter colors defined in the upper eight) and, 'pink' and
 'orange' to colors in 256-color xterm's default color cube.  These
 defined colors may then be used as any of the pre-defined eight,
 including appending '_background' to set the background to that color.