Two appearances were hard to tell apart. Magpie is meant to look like the signed-in site, but it was missing the soft coloured wash that the site paints behind its pages, so it read as a slightly flatter version of the default. It now carries that wash — the same one used by the Forms section itself — and the panel is translucent so the colour shows through, as it does elsewhere on the site.
The appearance called Default has been renamed Plain, which is what it actually is: a white card on a plain background. Its description used to say it was the current Magpie appearance, which stopped being a useful way to tell it apart once there was an appearance called Magpie. Nothing about how it looks has changed, and forms already using it are unaffected.