RGB vs CMYK Colorspace
In the design world, there are two main ways to mix color, and their differences can sometimes make it difficult to get the colors in the final product to look the way we want.
RGB is the mixing of red, green and blue points of light to produce colors on screens for computers and television. This is called an additive colorspace, which means that the more light on the screen, the brighter the image. When creating a design on the computer, all of the colors on the screen are produced by RGB.
CMYK is the composite of tiny drops of pigments for four-color printing, and is the industry standard. Because of the nature of light and pigment, CMYK is a subtractive colorspace, which means that the more ink on the paper, the darker the image will be. Because of this, CMYK can't reproduce all of the same bright colors as RGB, so your files may look different from the screen once they are printed. If you compare the above images, you'll notice a difference in the vibrancy of the colors.
When you turn in files to be printed, make sure that none of your images are RGB. You can do this in Photoshop through the image>mode menu. If you forget, we will take care of it, but be aware that color shift may occur. Quality proofs should be obtained to verify that colors are accurate.