This is week 4 of the HP Ink Challenge. I used ColorLok paper and generic copy paper and I didn't really notice a difference in the prints. When I turned the pages over, the ColorLok paper seemed to bleed through a little less, but not enough that would even show up if I took a picture of it. Having both paper I would probably choose the ColorLok to make a birthday card, but again both were up to my standards. :) I also printed the same documents I have each week and I still notice streaking in the the refill ink prints. HP ink is still solid. The HP ink prints more closely to the computer image. The refill ink is less vibrant. (picture on the right) I received two free HP Deskjet 3510 printers and supplies as well as a gift card to purchase refilled cartridges from HP in order to participate in the Ink Challenge. All opinions and views expressed are my own.