Open Radar

 
Summary:
After turning on "Page guide at column" in Xcode's preferences, the page guide darkens right side of the editor (see attached `actual_look.png`). While this might look kind of okay for some color schemes, it certainly looks bad for others. In addition, no other popular code editor does this, which makes Xcode stand out but not in a positive way.

Xcode 9 is a magnificent release that takes Xcode's code editing functionalities to the high standards. Given the news about complete rewrite of the source editor, I believe that now is the best moment to allow users to opt-out of (or disable at all) the aforementioned darkening functionality.

Steps to Reproduce:
Turn on "Page guide at column" in "Text Editing" tab in Xcode's preferences and open or create any source file.

Expected Results:
Page guide darkens the right side of source editor (see attached `actual_look.png`).

Observed Results:
Page guide is just a line and it doesn't darken right side of source editor (see attached `expected_look.png`).

Version:
Xcode 9.0 beta (9M136h), but the issue existed in earlier versions as well.

Notes:
Page guide doesn't darken right side of source editor in the most popular code editors and IDEs:

- Atom (https://atom.io)
- Sublime Text (https://www.sublimetext.com)
- Visual Studio Code (https://code.visualstudio.com)
- Visual Studio for Mac (https://www.visualstudio.com/vs/visual-studio-mac/)
- JetBrains AppCode (https://www.jetbrains.com/objc/)

Also, because I understand that some people might prefer the current behaviour, I believe it would be the best to make the requested behaviour opt-in (or opt-out) in Xcode's preferences (e.g. using a new checkmark option).

Configuration:
"Page guide at column" is turned on in Xcode's preferences under "Text Editing" tab.