So, I've been struggling with this Default Site Color Theme thing on 7.1
Maybe it's an old issue and I'm late to the party, but I finally figured out that my site was using the color theme "Light 2" as the default.
This was causing color issues with "gaps" in the layout (like below the footer of the site), loading lags, 404 page, and Product Detail Lightboxes.
I don't remember setting that theme as the default for the page, and I don't know how to pick a different default theme for the page, but I can at least correct the color issues by picking the colors in that theme.
*EDIT: Oh, and just rereading HerMessyBun's previous post, I see that they figured that out as well, but I didn't understand what they were saying until now.