phpBB Native Fulltext does not index and search for words enclosed between color tags.
For example,

[color=#0000FF]whatever word[/color]

in message will not be found.

it is related to function function split_message in phpbb/search/fulltext_native.php

If comment this regex

// BBcode

$match[] = '#\[\/?[a-z0-9\*\+\-]+(?:=.*?)?(?::[a-z])?(\:?[0-9a-z]{5,})\]#';

in 1328 line everything works well and the words between color perfectly search.