Can you get 720 drivers from HP that are designed specifically for XP? I'm not sure as this printer is now getting a little long in the tooth, but when I had a 720C I recall it wasn't too happy with the 98 drivers that Windows suggested and worked better with the genuine article. Whether or not this would account for the colour mixing, I'm not at all certain. It could be that the XP driver and printer don't get along or simply just age and wear and tear on the ribbon cable within the printer. By the time you've sampled a few more cartridges it may be more economic to buy a new printer (even though the 720C is a very good printer itself).
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