How would you like to stare at these colored lines all day?
I don't know exactly where they're originating. I used a pair of binoculars to zoom in on the affected pixels to figure out exactly what's going on screen-side. It turns out that the yellow bar is generated by the red and green subpixels for that column being stuck in the on position. The blue bar, as you may have guessed, is caused by the blue subpixels being stuck. Blue in the first bar and red and green in the second work as expected, so if I display pure white, neither of them appear. There's no such problem when using an external monitor over VGA.
The red line began sporadically appearing way back in June. I could usually fix it simply by tapping the screen lightly. Eventually this method became useless, as the red bar would show up again immediately after whacking the screen. The green subpixels in the same column then began to stick sometime in September. As of last week, the blue bar began to appear every five or so pixels, such that it appeared as a dashed line; the spacing between pixels gradually shrunk until the entire column displayed blue.
Has anyone seen this before, and if so, would they know what may be causing it? I'm extremely reluctant to send the laptop back to HP again, as there's a good chance they'd simply charge me $449 to replace the screen.