Microsoft continues to make changes to Windows 10 Mobile, even inside its own builds. The company released the latest version, build 10136, for Windows Insiders earlier this week and now the app store in that build has been updated to version 2015.5.29.1. The big change is a new dark theme for the store that appears to be the default.
The dark theme is certainly a big help in making images and logos pop out of the store. It's unknown if Microsoft will keep the theme as the default when Windows 10 Mobile launches officially sometime later this year.
Thanks to 12ColourPencils and Montpbm for the tips!