DVD blue lines

Can anyone tell me why there are faint thin blue lines along the edges of the letterboxes when DVDs are played? I thought it was just mine, until I went to a Target the other day in which one of those giant dispalys of numerous TVs were all playing the same DVD, and every TV had the lines. The lines are very faint, but you can mostly notice them up against brown backgrounds. Any ideas? Thanks.

It could be the way the movies were created and/or something to do with the DVD players. Probably best to ask at Target and see if they know. Mind ya, they’ll probably say they can’t see the blue lines :/