I would like to gray out a column (e.g., column H) based on who opened this document - as in based on the Google account that is viewing or editing this google sheet.
As you could see in the below picture, I want column H grayed out (not hidden but disabled for user input) when anyone else other than a specific person is viewing/editing it. 
Take a look at protecting ranges, it will provide with just what you need to avoid users from editing a particular range of the sheet. In short, it work similar to file permissions, you can assign edit permissions in particular ranges so that only you (assuming you're the file owner) can edit in that range.
As for the coloring, I would advise against this, it could be achieved with a script, but if two users have the Sheet open at the same time (one with permissions, one without) one of them will see the column in a way they shouldn't. If you set the protected ranges, they will see a window telling them they cannot edit that cell.
