This provides any color of border around the active window if it is sandboxed. Each sandbox can have its own border color for easy identification.
It is written in Autohotkey with the source code included in the zip.

Download
Sandboxie borderGuard thread
To add a red border for a sandbox called 'test' put this in your ini file:
Code:
[test]
borderColor=0xFF0000
You can also use color names instead of RGB values for any colors, default or per sandbox. EG: red, blue, green (see
HERE for complete list.)
Global Options are:
- Sandbox Path
- Hide Border on Drag
- Fancy or Square Borders
- Left Offset
- Menu Localization
- Border Color
- Border Thickness
- Border Transparency
Per sandbox options are:
- Border Color
- Border Thickness
- Border Transparency
TODO:
- When changing sandboxes, the border appears with the color of the last sandbox briefly before changing to the correct, new color. Need to fix this!
- Maybe make Fancy Borders a per sandbox option.
- Gui for settings instead of just ini.