For those particularly concerned with exactness of color output, it is important to submit a color-managed file.
To embed a working space in Photoshop or Illustrator:
Open the file.
Click: Edit » Assign Profile.
Choose the appropriate working color management profile for the color space of your file.
For RGB files, use "sRGB IEC61966-2.1"
For CMYK files, use "U.S. Web Coated (SWOP) v2"
We do not recommend switching color spaces.
Please note, that if the file was not color-managed from the beginning of its creation, or if it was created by an application that does not manage color (such as any Microsoft Office software, like PowerPoint or Publisher) then there is no consistently applicable workflow that can ensure color accuracy, and file-to-print results will be unpredictable