I am running Byobu on my server and it looks good with the exception of my OS X terminal confusing the blacks. I remember seeing somewhere you can change some mode and the colors actually look right, do you know what option that is?
I don't have access to an OSX machine, but you can try tweaking the black that's used for the status bar at the bottom.
You'll need to edit the file
That's from a lower case to an upper case 'K'.