Discoloured chrome parts

I got one of AMT's 67 impala street machines with the intentions of making it sorta stock looking but when I had a look at the parts in the box I notices that the bumpers of the car are discoloured toward the bottom (They are discoloured from the top of the bumper to the bottom). they go from chrome and toward the bottom go a kinda green chrome like colour... Anyone else had this problem with chrome parts?? I tried to do some BMF fixing but don't have the patience to get it nice and wrinkle free. Any way of fixing without the use of chrome paints?

Any help would be appreciated, I'll post a pic of the parts a bit later...

Source: http://cs.scaleautomag.com/SCACS/forums/thread/992555.aspx

Nicolas Kiesa Leo Kinnunen Danny Kladis