Animation of a circle in iOS - ios

Question

I'm learning how to use SpriteKit and would like to have a circle that:
Grows and shrinks smoothly
Pulses with a colour
Is displayed with crisp edges
So far, I've come up with the following code:
import SpriteKit
class GameScene: SKScene {
override func didMoveToView(view: SKView) {
addCircle()
}
func addCircle(){
let circle = SKShapeNode(circleOfRadius: 50 ) // Size of Circle
circle.position = CGPointMake(frame.midX, frame.midY) //Middle of Screen
circle.glowWidth = 0.0 // No border
circle.fillColor = SKColor.yellowColor() // Start as yellow
let actualDuration = 1 // Animate for 1s
// Basic actions for grow, shrink, colour up, colour down
let actionGrow = SKAction.scaleTo(CGFloat(2), duration: NSTimeInterval(actualDuration))
actionGrow.timingMode = SKActionTimingMode.EaseInEaseOut
let actionShrink = SKAction.scaleTo(CGFloat(0.5), duration: NSTimeInterval(actualDuration))
actionShrink.timingMode = SKActionTimingMode.EaseInEaseOut
let actionColorUp = SKAction.colorizeWithColor(UIColor.redColor(), colorBlendFactor: 1.0, duration: NSTimeInterval(actualDuration))
let actionColorDown = SKAction.colorizeWithColor(UIColor.redColor(), colorBlendFactor: 0.0, duration: NSTimeInterval(actualDuration))
// Combine the actions
let actionGrowWithColor = SKAction.group([actionGrow,actionColorUp])
let actionShrinkWithColor = SKAction.group([actionShrink,actionColorDown])
// Run and repeat
circle.runAction(SKAction.repeatActionForever(SKAction.sequence([actionGrowWithColor,actionShrinkWithColor])))
// Add the circle
self.addChild(circle)
}
}
The first of my three criteria are met, but the other two are not.
As the SKShapeNode is not a vector, as it grows the edges are not crisp. Is there a better way to draw a circle, or should I just start with a circle that is sufficiently large?
Is there a reason why the colorizeWithColor section doesn't appear to have any effect?
Many thanks in advance!