https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html describes in the section "Implicit Member Expression" that
An implicit member expression is an abbreviated way to access a member of a type, such as an enumeration case or a type method, in a context where type inference can determine the implied type
While https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Methods.html states
Classes, structures, and enumerations can also define type methods, which are associated with the type itself. Type methods are similar to class methods in Objective-C.
Thus it is expected that the UIButton method
func setTitleColor(color: UIColor?, forState state: UIControlState)
should be callable as follows, assuming a UIButton instance of redButton
redButton.setTitleColor(.redColor(), forState: .Normal)
Currently, as of Xcode 6.3.1 (6D1002), this statement will cause swiftc to crash.
Open ImplicitMemberExpression.playground in Xcode 6.3.1 (6D1002) and uncomment the line
// button.setTitleColor(.whiteColor(), forState: .Normal)
UIKit methods with explicit type parameters (e.g. not AnyObject) should work with Implicit Member Expressions without causing compiler crashes, even if the type parameter is optional.