Custom color my UIActivityIndicatorView
In iOS 5.0 and up you can use setColor: on the UIActivityIndicatorView to set a custom color.
In Swift you can just use activityIndicatorView.color = UIColor.red
You need to create a custom set of images (better), then animate it using a UIImageView.
Or place a colored transparent view on top of the activity indicator to "tint" it (lower quality).
For Xcode 7 (possibly earlier) you can also specify the color directly in Interface Builder.