in v.3 this was available via a custom bar. I had several colored highlighters for one-click functionality. As a matter of fact, we even had Ctrl-H (or whatever other combination you chose to select - I also had Ctrl-G for Green) keyboard shortcut to highlight words on-the-fly.
Sure miss those good ol' days (is there a smiley simbol for a sad puppy dog look?)
Actually, if someone knows how to do it in Logos4 this would be awesome to know. I use this tool a lot. If it is not currently available - I'd like to make a suggestion to put it on "add these missing v.3 features sooner-rather-than-later" list.
Vladimir
