It is very common for a refilling process to introduce air bubbles into your HP 901 cartridges. Air bubbles block ink flow to the printhead temporarily, causing the printer missing a color or printing in stripes. To remove the air bubble, you can let the cartridge sit for few hours, even overnight. Printhead cleaning will make the process faster.
From the HP Solution Center,
1) Click the Settings menu, point to Print Settings
2) Click Printer Toolbox
3) Select "Device Services"
4) Select Clean the Ink Cartridges.
The process is on page 65 of your HP owner's manual. You can find a copy here: http://www.hp.com/ctg/Manual/c01770356.pdf