how to structure the init method of a custom shape class

C4WorkSpace.m

//
//  C4WorkSpace.m
//  customShapeInit
//
//  Created by Travis Kirton on 12-04-30.
//  Copyright (c) 2012 POSTFL. All rights reserved.
//

#import "C4WorkSpace.h"
#import "MyShape.h"

@implementation C4WorkSpace

-(void)setup {
    MyShape *ms = [MyShape new];
    [ms ellipse:CGRectMake(100, 100, 100, 100)];
    [self.canvas addShape:ms];
}

@end

MyShape.h

//
//  MyShape.h
//  customShapeInit
//
//  Created by Travis Kirton on 12-04-30.
//  Copyright (c) 2012 POSTFL. All rights reserved.
//

#import "C4Shape.h"

@interface MyShape : C4Shape
@end

MyShape.m

//
//  MyShape.m
//  customShapeInit
//
//  Created by Travis Kirton on 12-04-30.
//  Copyright (c) 2012 POSTFL. All rights reserved.
//

#import "MyShape.h"

@implementation MyShape
-(id)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if(self != nil) {
        self.animationDuration = 0.0f;
        self.fillColor = [UIColor purpleColor];
        self.strokeColor = [UIColor greenColor];
    }
    return self;
}
@end