Flights are available with Easyjet to Dresden or Rheinjet.de have started a Barcelona - Altenburg route like Ryanair had.
Ryanair and Airberlin fly to Leipzig. It is then a short drive from the airport.
Flights are also available to Hannover with British Airways or to Berlin regional airports with British Airways, Ryanair and easyjet. This would be a self drive option as are approx. 2 to 3 hours drive from Colditz.