As mentioned previously, we are offset printing, which is traditional printing on large presses (Heidelbergs, for example), but we are also gang printers. Gang printing is the process of placing 100s of files on a large sheet and colour is considered pleasing (not an exact match). This also means that colours will shift from order-to-order and sometimes even on the same run if you are ordering a number of employees for the same company, i.e. we cannot always guarantee that we can keep all the cards on the same sheet or that “neighbouring files” will be comlementary to your colours. Many times, colours compete with each other, making it impossible to colour match every time.
To learn more about Gang Printing, see this Wikipedia article.