There are a couple of reasons that cause color shift on printed discs.

1. On short runs (less than 1000); it takes approximately 30 to 45 minutes to set up the press and then only a couple of minutes to print the entire job (100 takes less than 2 minutes).  This allows very little time for the operator to adjust colors via the press on board computer.  Usually color adjustments are made gradually over a quantity of several hundred discs, on short runs we are forced to make more aggressive color adjustments over a quantity of only 25 to 50 discs.
2. There is very little color control the operator has on the press and un-like traditional offset printing on paper, there are no color bars or registration marks to assist the operator.
3. When the artwork has a big difference from the lightest color to the darkest color when one color is adjusted it affects the other color and because of the difference between the lightest and darkest color any variance is more noticeable to the human eye.  For example trying to match a area of cmyk for a corporate logo and still match the other elements.  Printing on media works best on photo images that color change is less noticeable to the human eye.
4. As standard procedure we try to maintain a 3 to 5 percent variation on a print run as specified by the press specifications.

These are pretty standard for all media offset printers no matter the brand.  We are constantly working with the manufacturer to improve our ability to print media in a more consistent fashion.