Printing is done using CMYK (Cyan, Magenta, Yellow and blacK) inks, so if you supply your images in RGB (Red, Green, Blue) they will be automatically converted to CMYK.
RGB (Red, Green, Blue) creates color by combining different colors of light. If you look very closely at a TV or computer monitor, every image is made of dots of Red, Green, and Blue lights. If you are creating an image to be displayed on a computer, TV, or lighted sign, you would use RGB mode to specify your colors.
Alternatively, printing is done by combining Cyan, Magenta, Yellow, and blacK inks to produce the colors you see. These inks on a cardboard surface don't have the intensity of a light source and are made of different combinations of colors. RGB colors can appear duller or less saturated when printed in CMYK, and in some cases there is not a clear, single equivalent of an RGB color in CMYK, so color shifting can also occur.
This is why we strongly recommend that you provide your artwork in CMYK. If you do any needed conversions yourself, you can then adjust the colors after conversion to appear much closer to your desired result.
Some software programs, such as Adobe Illustrator and Adobe Acrobat have built-in functionality to better represent CMYK colors on computer monitors. If you have one of these software programs installed on your computer, that should help you convert and preview the artwork with better accuracy.
While we are unable to guarantee color matching, the vast majority of our customers are pleased with the final appearance of color on their printed boxes.