One issue that comes up quite frequently, is the difference between RGB and CMYK. If you're unfamiliar with these terms, please refer to our Glossary of Terms in the column to the left. It will help to explain to you the difference, but in a sense everything that runs through the printing process goes throgh as CMYK.
Another issue is that what you see on your monitor screen isn't always the way that it will appear on your printed piece. Everyone's cameras' settings can be set differently, their monitors can be adjusted differenly, everyone's eye's can see the image differently and lighting in the office can certainly affect the way things are viewed.