Transparencies in files
Transparent objects and digital printing don't mix. Transparencies can cause issues with overprinting, changing colors or even blocking entire areas of your file. If you're adding an image to your design, make sure to flatten the transparency so it will print the way you intend.
Here’s what you do:
1. Open file in Adobe Illustrator
2. Select all (of the design)
3. Go to top menu bar and choose Objects, then scroll down to Flatten Transparency
4. A new window pops up. Choose High Resolution and click Ok to save
Easy, right? It's best to take that extra step to make sure your files will print correct.
Want more info? Here's a blog post explaining this process with awesome screen shots to boot!