help: update the color documentation for Windows 10 ANSI support

It looks like only the initial release of Windows 10 lacked support for this
functionality. [1][2]  Since that build is no longer supported, I didn't bother
getting very specific, to keep the help text less cluttered.

[1] https://github.com/symfony/symfony/issues/17499#issuecomment-243481052
[2] https://en.wikipedia.org/wiki/Windows_10_version_history

mercurial/help/color.txt

@@ -22,7 +22,8 b' See :hg:`help config.ui.color` for detai'
   The default pager on Windows does not support color, so enabling the pager
   will effectively disable color.  See :hg:`help config.ui.paginate` to disable
   the pager.  Alternately, MSYS and Cygwin shells provide `less` as a pager,
-  which can be configured to support ANSI color mode.
+  which can be configured to support ANSI color mode.  Windows 10 natively
+  supports ANSI color mode.
 
 Mode
 ====

mercurial/help/config.txt

@@ -415,7 +415,7 b' effect and style see :hg:`help color`.'
 ``mode``
     String: control the method used to output color. One of ``auto``, ``ansi``,
     ``win32``, ``terminfo`` or ``debug``. In auto mode, Mercurial will
-    use ANSI mode by default (or win32 mode on Windows) if it detects a
+    use ANSI mode by default (or win32 mode prior to Windows 10) if it detects a
     terminal. Any invalid value will disable color.
 
 ``pagermode``