The blue ones with white text (occasionally another grapheme but usually text) are beta sites. Nearly all beta sites use the same site style. Coffee and 3D Printing are beta sites.
When a site graduates, one of the designers on staff will work with input from the community to develop a complete custom design for that site, including the icon. The other sites in your screen shot are graduated sites.
Recently it has become possible for a site to graduate without yet having its new design, so you'll see some blue-and-white logos that aren't beta sites while their designs are produced. So not all sites using that scheme are beta sites, but all beta sites use that scheme.
("Nearly all:" CraftCMS is in beta and does not use the white-on-blue scheme. I don't know how that came to be. But if you scan the list of all sites, you'll see that the vast majority of beta sites are as I described.)