I have a logo with white text and a transparent background. The site is a dark theme. When Facebook and Google+ brings in my links. It is quite hard to see the logo. Is there way to tell these services to use a version of the logo with black text, so it's visible?
You can either edit your image, like bybe says, or you can tell Facebook and Google Plus which image to use by using the Open Graph Protocol. If you create a new image and add it to the
meta property="og:image"-tag, they should use that image when people share one of your pages.
If you use this, you won't run the risk of Facebook or Google using the wrong image and you won't have to edit the image again if you ever decide on a different background color for your site.
This is happening because your logo is a transparent PNG file which is normally fine but because your logo is white it will clash with Google Plus as they use a white background. A simple fix to this solution is to edit your PNG file and give it a solid background color the same of your elements on the website, in this case a background of #212121.
It's worth noting that Google Plus will only use your logo when another image is not offered on the page.