MKPinAnnotationView: Are there more than three colors available?

You could use ZSPinAnnotation to create annotation pins on the fly with a specified UIColor: https://github.com/nnhubbard/ZSPinAnnotation

some more ;)

And the original ones :

And the code:

- (MKAnnotationView*)mapView:(MKMapView*)mapView viewForAnnotation:(id <MKAnnotation>)annotation {
MKPinAnnotationView* anView =[[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"test"];
anView.pinColor=MKPinAnnotationColorPurple;
UIImage* image = nil;
// 2.0 is for retina. Use 3.0 for iPhone6+, 1.0 for "classic" res.
UIGraphicsBeginImageContextWithOptions(anView.frame.size, NO, 2.0);
[anView.layer renderInContext: UIGraphicsGetCurrentContext()];
image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
NSData* imgData = UIImagePNGRepresentation(image);
NSString* targetPath = [NSString stringWithFormat:@"%@/%@", [self writablePath], @"thisismypin.png" ];
[imgData writeToFile:targetPath atomically:YES]; 
return anView;
}

-(NSString*) writablePath {
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
return documentsDirectory;
}

You might find the following images useful:

and the code to use them in viewForAnnotation:

- (MKAnnotationView *) mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>) annotation
{   
    // ... get the annotation delegate and allocate the MKAnnotationView (annView)
    if ([annotationDelegate.type localizedCaseInsensitiveCompare:@"NeedsBluePin"] == NSOrderedSame)
    {
        UIImage * image = [UIImage imageNamed:@"blue_pin.png"];
        UIImageView *imageView = [[[UIImageView alloc] initWithImage:image] autorelease];
        [annView addSubview:imageView];
    }
    // ...