Glad to hear that got you going with the #100 error and thanks for pointing that out!
Unfortunately, you can change the font-color of the module. The options present for border and background color are all that Facebook provides, and therefore, all we can provide. You can see their configuration tool on the page below if you'd like to see/test the options:
developers.facebook.com/docs/reference/plugins/like-box/
We've heard of users preferring the "Light" color scheme on dark sites for just this issue. We'd really like it if Facebook had a way to override their styles, but they don't offer that capability anymore. They used to, a few years ago, but it was abused in such a way that Facebook removed most of the customizations possible.
The other option would be to set a different background color for that module position in your template's CSS file. We can help with that if you have any questions, and is the best advice we can offer.
Hope that helps, and good luck,
Alex