This file is indexed.

/usr/share/zsh/help/colon is in zsh-common 5.1.1-1ubuntu2.3.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

1
2
3
4
: [ arg ... ]
       This command does nothing, although normal  argument  expansions
       is performed which may have effects on shell parameters.  A zero
       exit status is returned.