The screen shot shows the current version of the main IDLE window, with the little pics at the bottom indicating what it looks like when the window loses focus.  A few entirely cosmetic changes I'd like to make here:

1. Swap scrollbar for ttk scrollbar; this visually will affect the Linux version. Note that even the ttk scrollbar is somewhat out-of-date with current desktops, but it's a step in the right direction!

2. You'll notice the slight border around the text widget when active; barely visible on Windows, a bit more so on Linux, and very much there on Mac (this is the "highlightthickness" attribute). Current conventions on all three platforms do away with this, so it should be removed for IDLE.

3. Regarding the items in the status bar, I'm going to suggest removing the sunken reliefs around the two items. Again, this was all the range long ago, but most apps on all platforms now have more minimal decorations in those contexts. If there were more (different) things on the status bar, I might suggest a light vertical separator between sections, but here there's no need for decoration at all.

4. Color and border on status bar. It's most apparent on the Mac inactive window pic, where the status bar blends in to the editor. I plan on tweaking the status bar so it's always a light grey color, and has a small darker separator above it. I may see about tweaking the font, as status bars tend to use a slightly smaller font nowadays.

5. Spacing for icon size grip on Mac should be removed for recent versions of OS X. This hasn't been necessary since before OS X Lion (released 2011). I can have the code include it when running on earlier versions of OS X.

These are all tiny changes, but combined with a decent font make a big difference visually when IDLE first starts up.