数値をちょっと変えてみたい時とかにいいですね

import UIKit
import XCPlayground

let view = UIView(frame: CGRect(x: 0.0, y: 0.0, width: 200, height: 200))
XCPlaygroundPage.currentPage.liveView = view


class customLayer : CAShapeLayer {

    override init() {
        super.init()
    }

    override init(layer: AnyObject) {
        if let layer = layer as? customLayer {
        }
        super.init(layer: layer)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func drawInContext(ctx: CGContext) {
        //背景
        let c = UIColor.whiteColor()
        CGContextSetFillColorWithColor(ctx, c.CGColor)
        CGContextAddRect(ctx, self.bounds)
        CGContextDrawPath(ctx, .Fill)


        for(var i : CGFloat = 0;i<360;i+=1){
            let cc = UIColor(hue: i/360, saturation: 1.0, brightness: 1.0, alpha: 1.0)
            CGContextMoveToPoint(ctx, 100, 100)
            let sa : CGFloat = i * CGFloat(M_PI/180)
            let ea : CGFloat = ((i + 1) * CGFloat(M_PI/180))

            CGContextAddArc(ctx, 100, 100, 100, sa, ea, 0)
            CGContextClosePath(ctx)
            CGContextSetFillColorWithColor(ctx, cc.CGColor)
            CGContextDrawPath(ctx, .Fill)

        }
    }
}


let c = customLayer()
c.frame = view.frame
view.backgroundColor = UIColor.blueColor()
view.layer.addSublayer(c)
c.setNeedsDisplay()

参考

UIBezierPath with color gradient

XcodeのPlaygroundをつかってUIの実装をサクサク試す