It could be due to a number of reasons, like the two previous posts suggested, you could try setting the printer to use less ink.
It could also be the type of paper you are using, maybe try using a different make/type of paper, and make sure you choose the correct paper type within the printer settings on your computer.
I would say that it could also be the ink but with you using genuine HP ink it is probably unlikely.
It could be any of the above or that the print out just need a bit more time to dry.