I have started teaching myself some Objective-C which also means that I have to use something else than my beloved Qt Creator.
As to feel a bit at home I have ported my Gulf theme over to Xcode. The choice I have made in creating this theme is to conserve all of the colours from the original (e.g. Types and Classes are greenish, while attributes are blueish).
Sadly Xcode does not provide different colours for global and local variables. However, all externally imported classes, types and functions are marked in italics, so you can easily know what belongs to you.
Here is a quick look at the theme:
And here is the download link, enjoy: