Adobe Illustrator PDF Works, but then uploading it changes colors

I searched through the forums and couldn't find an answer to this specific question, so here we go:

I've designed a business card in illustrator. The background is a darker red. I export as a PDF and it looks great. Here's what the PDF looks like:

The problem is when I upload it to the card printing site (I'm using got print) the upload has a solid black background, like so:

So, is the site just displaying it funny and they should print fine? Or am I doing something wrong? I've made sure it's CMYK not RGB, but I can't figure out what I'm doing wrong.

Any help is greatly appreciated, thank you!