Juice Drops: Juice Drops colors shift when printedSee All Topics for Juice Drops
Computer monitors generate colors using red, green and blue colors. (RGB)
Professional printers use a different method. They use four colors - cyan, magenta, yellow and black. (CMYK)
It is possible to create colors in the RGB color space that are not printable in a CMYK color space. These are called "out of the CMYK color gamut". In many cases a 100% blue may appear as purple when printing in CMYK.
In programs like Photoshop you can adjust the color space to see how an image will look in CMYK before sending it off to the printer. With your image open in Photoshop, from the menu select Image->Mode->CMYK Color. If you have a layered image, then you will be prompted if you would like to merge the layers first. Some compositing modes are affected differently when changing color space, so you might want to experiment with this.
You should notice a bit of difference when you change the color space from RGB to CMYK. Adjust the color of the image (or just a layer if needed) while in the CMYK color space so that it better represents the original RGB image.