I have almost the same problem as Zulkarnine, and the previous solutions didn't work for me =S
The difference is that i have color and auto-complete code with:
pinMode(myLED, OUTPUT);
but i don't have with this:
Serial.begin(960);
As I wrote before,
Code-sense, auto-completion and arguments list are displayed usually without problem in my laptop.
Now, it isn't a 100% hit because code-sense implementation changes with every Xcode release and as Apple is more than secretive about the customisation of Xcode.
Xcode code-sense doesn't seem to be powerful enough to manage
virtual functions within classes. Serial.print() is a virtual function.
=S anyway, Is there any theme to get the color equal to the arduino ide?
Sorry, but I can't provide support for Xcode. Please refer to Xcode documentation for interface customisation.
I strongly recommend you to refer to the book
Xcode 4 Unleashed by Fritz F. Anderson I purchased thanks to
contributions.

Good luck!