colors/fonts change once test email is sent

I recently created a new campaign that looks fine in all of the preview tabs (including mobile). However, upon sending the email, the fonts and colors come out completely different. 
For example, the text is supposed to be white, but in the test email, all of it is black. The background is also a completely different shade of red than the one I selected in the preview. 
The logo, which is supposed to be transparent, comes out with a gray background and is formatted incorrectly. 

I've found some people with similar issues in the forums, but have yet to figure out how to resolve this.