We do ask all custom uploaded files to be designed in CMYK, and uploaded in CMYK. You may also upload in RGB if you choose, however the color will be converted and may not be as accurate. If your file contains large quantities of blues and purples, it may be best to limit the magenta hues in the design by at least 10%. If you do upload in CMYK, we ask you to design using our preferred color profile for better color accuracy. If you have any questions, please view the link RGB VS. CMYK for more details
