How can I change the color of invisibles in Xcode4?
If your version of Xcode has the option to change the color of the invisibles, that (probably) doesn't actually change the color of your spaces. I can't be sure because I have Xcode 4.6.
Try the following:
1. Open the Fonts & Colors preference pane with Command+,
2. Change the color of the invisibles
3. Editor menu > Show Invisibles
4. Check if the color of the symbols representing tabs and spaces match
5. Change the color in the preferences again
6. If the color of the little symbols change, it means I correctly imagined your version of Xcode.
Hope this helps.