I have uploaded a preliminary version of OpenMeta for Mavericks.
Basically, On Mavericks, Apple has added a new get/set tags API.
The Apple API seems to work, but has some issues with colour and changing colours of tags, etc. Indeed, there is no official Apple API for setting or getting the colour of a tag, so I have left that out for now. Basically you set tags, then in the Finder you can assign a colour to any tag you set in OpenMeta. There are ways to do this at a low level, and perhaps it could be added to the OpenMeta API. Please talk about that.
I am unsure about wether to add a migration task for moving tags from 10.7 - 10.8 to the new Apple format. The way my apps worked it was automatic on launch.
Calling OpenMetaSync will do a conversion, as calling getUserTags on 10.9 makes sure that the tags are set so that older and newer systems can read them.
You can call OpenMetaSync to do a conversion even if you don't want to create a backup file.
Launching Leap or Yep 3.5 (available as soon as XCode5 / 10.9 is stable enough that Apple allows it to ship applications with), will also update all tags to Mavericks tags.
--Tom