I use to have the same (similar?) problem after updating from 12.10 to 13.04.
These flickering lines appears straight at the log-on screen
This is what I do, to make my screen to be back in shape and colors: Right after hearing that little drum sound, enter my password and press Enter. The flickering is NOT gone just yet, so I log-out. Press Alt+Ctrl+Del and then Enter again.
This how I'm again on the Log-on screen, but this time everything is fine. Log in and enjoy your Ubuntu! ;)
And this how I have to do every time I power on my laptop. My experience tells me that this could be due to video card or it's driver incapability issue. Perhaps, that's why I leave it as it is... I have ASUS A8j witch has graphics by nVidia, unfortunately...
Hope this helps in some way to you.
Is not flickering anymore (as for me). Perhaps been fixed with the latest updates... Thanks :)