If its on every screen including when the rom isn't loaded, like in recovery or during a reboot - then it's most likely a row of dead pixels. If it's just on that specific screen, then it's most likely a corrupted picture for either the buttons or the lockscreen wallpaper
It is not there once you unlock the device....... but, ...... it is happening on every rom you flash.......
I think I would just wipe everything, about 5 times. Backup, Reformat and repartition the sd card and only copy back what files you really need and nothing system related and see if that fixes it.
I had something similar on my Mytouch3g (It had a series of pixelated dots that might make you think you had bad pixels, but only on main screens, once you launched any program they went away and worked fine).
I also had a line problem with color on the N1 on the lockscreen (not like yours, similar, but a pink blurry line). What fixed it for me in both cases was major wipe of everything including the sd. I flash a ton of roms, all the time, and so I am thinking that some small bits of code get left somewhere occasionally to cause odd things like this. Other than the inconvenience of reloading everything, it can't hurt to try.
Not saying that will fix your problem, or that it is even related, lol, just saying what worked with me.
In any case, good luck, I hope you get this resolved.