Don't force colour in aliases.

* gnu/system/shadow.scm (default-skeletons): Substitute ‘--color=auto’
for ‘--color’ (which implies ‘=always’) in aliases.
* doc/guix.texi (G-Expressions): Also adjust examples as that makes
more sense.

doc/guix.texi

@@ -5464,7 +5464,7 @@ denoting the target file.  Here's an example:
             `(("hosts" ,(plain-file "hosts"
                                     "127.0.0.1 localhost"))
               ("bashrc" ,(plain-file "bashrc"
-                                     "alias ls='ls --color'"))))
+                                     "alias ls='ls --color=auto'"))))
 @end example
 
 This yields an @code{etc} directory containing these two files.

gnu/system/shadow.scm

@@ -178,9 +178,9 @@ then
 else
     PS1='\\u@\\h \\w\\$ '
 fi
-alias ls='ls -p --color'
+alias ls='ls -p --color=auto'
 alias ll='ls -l'
-alias grep='grep --color'\n"))
+alias grep='grep --color=auto'\n"))
         (zlogin    (plain-file "zlogin" "\
 # Honor system-wide environment variables
 source /etc/profile\n"))