Question: I am looking for a visual tail tool that can monitor several local or remote log files.

Optional features that interest me: color highlight based on log error level, coloring for special words, filtering of messages and/or notifications on new activity.

Answer: 
You may try to use a combination of `multitail` and `ssh`.

* <https://serverfault.com/questions/53976/use-local-tools-to-monitor-remote-logs>
* <https://superuser.com/questions/320575/mac-os-x-logfile-viewer>
While I haven't used it myself yet, I recently discovered [Log.io](http://logio.org/). It appears to meet all your criteria.