In a C# using block, eg.
static void Main(string] args) {
using (var x = new FileStream("Foo.txt", FileMode.Open, FileAccess.Read)) {
var b = x.ReadByte();
}
using the default (as installed) C# language file (…\Sublime Text 2\Packages\C#\C#.tmLanguage) the using keyword is not highlighted as such. It should be treated as the “lock” in a lock statement block.