A really good technician is a treasure. I've met technicians who are brilliant at diagnosis and repair, and I always do my best to keep in touch with them. If you can find such a person, their expertise is invaluable.
Unfortunately, a lot of technicians have limited skills, and don't understand just how little they really know. When one of them starts to fool around with a moderately complex device, the chances are high that it will end up in worse shape then when it left the factory. That's why I always do everything I can as an end-user before calling in a technician, even for something that's still under warranty. I'll put up with minor deficiencies in a product, rather than taking a chance with warranty "repair".
As David says, running cleaning cycles isn't always a great idea, because firing all of the nozzles in a channel can spit out more ink than the ink delivery system can supply to the head (but maybe not in this case, if most of the nozzles are clogged).
I think that patience can sometimes accomplish what a service visit can't. A service technician can't afford to sit around for hours, wondering whether a gentle soaking would clear up a clog. Depending on your production schedule, you might not be able to either - but if you can, I'd be inclined to take things slowly. If you have the luxury of time, you could consider overnight exposure to distilled water or a cleaning solution, followed by a pair clean, followed by printing a dozen sheets of paper that are mostly the missing color, followed by a rest. Repeat daily until you run out of patience, or the problem clears up.
As a user, you can spend more time thinking about a problem than a service technician is likely to. You can peer at the capping station with a flashlight, and see if there's anything different about just one color. You can look back at your saved stack of dated nozzle checks, and see if there's a pattern to your clogs. You can try to correlate problems with things you've done to change the machine environment, like changing an ink cart.
Importantly, you can make the service technician sit down and talk to you before you allow him or her to touch the machine - and if you don't like what you hear, don't be shy about sending that person back with instructions to return with someone who is more knowledgeable about your machine. If the field office has several technicians, it's most likely that they will start by sending you someone who isn't in huge demand - and the best technicians will always be in demand.