Go to Google Images and type "vertical bar on lcd". But most of them are pure white or pure black and were due to disconnected data lines on the ribbon cable, meaning nothing got drawn there at all.
I've never heard of your issue where something IS drawn but is drawn darker.
Maybe a loose ribbon cable, maybe a faulty video chip, maybe they use panels for backlighting and one is darker than the others etc...
Afraid I can't help more than this...