On occasions I have been asked to troubleshoot Canon printers that have print heads that are of the type that are used in the i865, Pixma iP4000 and iP4200 (and possibly other Pixma) Canon inkjet printers. Some problems are evidenced by printed pictures that are overcast by a colour such as green or purple and/or by the failure of some colours (including black) to print satisfactorily in the Canon Maintenance application's Nozzle Check. Such problems often arise when the printer has not been used for a long time and the print head for one or more of the colours has clogged up. Clogged print heads are often caused through under-use so that things dry up and block.
Another symptom of clogged heads is a banding effect that is most obvious when "plain paper" is the selected print medium. That can look like this (as a result of a clogged Cyan print head):
To avoid cloggage I recommend exercising the printer at least every week. At least run the Canon Properties / Maintenance / Nozzle Check function a few times and print a test page that exercises all the colours. The Digital Dog Printer Test File downloadable from a link in this article http://www.normankoren.com/printer_calibration.html is an excellent test page that I use for that purpose.
If the Nozzle Check generates unsatisfactory results try the Canon "Deep Cleaning" maintenance routine. That's accessed through printer Properties / Maintenance / Deep cleaning. Then try the Nozzle check to see what colour or colours are not printing correctly. A number of repeated deep cleans and nozzle checks may indicate that there are problems with a single colour, or multiple colours. That may lead you to replace one or more cartridges to see if the problem was a cartridge rather than clogging in the print head/s. If that fails, read on.
A search on the web shows that a number of methods are advocated for cleaning print heads. This includes, for example use of water, isopropyl alcohol, glycol and windex. Some physical methods advocate use of high pressure water, compressed gas and an an ultrasonic cleaner.