The colors in your proof may look different from the original artwork for many reasons. The most common reason has to do with how screens represent color vs how printed goods represent colors. Real-life color is never like what we see on TV or a computer monitor, it renders your eyeball and brain differently. If your original art file was built using an RGB or Pantone color mode, we must convert it to CMYK in order to print. This will cause the colors to dull and soften compared to the RGB version.
We print using CMYK color values, while screens represent color in RGB values. This means that your items will likely always look brighter and more vibrant when looking at a screen versus when looking at them in your hands after they are printed. We do our best to color match when possible with CMYK values, however, we do not have the ability to 100% color match.
Looking for a more in-depth explanation of the different styles of color printing? Check out this resource!