I really hate to say that it looks like the printing is completely intentional, but that the photos here are incredibly misleading. I didn't purchase the Imperial Family mat, but I can tell by looking at the review photos that it's not printer defect, unfortunately. I don't know if Drop was provided the photos, or if they took them personally, but whoever is responsible for them needs to own the fact that they're not accurate.
Also, it really sucks that the only way any of you would've known this was if you viewed the Geekhack thread from back in July, where they show a photo of the final product:
No worries! I owe a big thank you to you for standing with our design and helping to explain it really well to the public just by looking at pictures. Thank you once again.
jessphangkeyNo thanks required, but I appreciate the kind words. I just have a lot of experience with all aspects of the art, design, and print process, so I just kind of wanted to help others understand what happened.
Be warned.
The white and gold mats are shipping with black spots not reflected in the photos. (See reviews).
Edit:
These spots are intentional but the product photos didn't reflect them.