How can I print photos properly (they come out as negatives)?

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http://askubuntu.com – I have a HP 845c printer and printing text, documents even non photo pictures works ok. However when I try to print photos, they come out like negatives with the colours all wrong. I'm on 12.04. I have the latest hplip installed. On windows it prints fine so there are no problems with the printers or ink. I'm not sure how to debug it further. Can anyone help? (HowTos)