请尝试以下代码：

func sliderValueDidChange(sender:UISlider) {
     print("value--\(sender.value)")
     if sender.value <= 0.3 {
        brokeSlider.minimumTrackTintColor = UIColor.green
     } else if sender.value > 0.3 && sender.value <= 0.6 {
           brokeSlider.minimumTrackTintColor = UIColor.yellow
     } else {
          brokeSlider.minimumTrackTintColor = UIColor.red
     }
}

试试看：

import Foundation
import UIKit

class AnnotationPhotoWidget: UIViewController  {
    let brokeSlider = UISlider(frame:CGRectMake(5, 440, 355, 20))

    override func viewDidLoad() {
        brokeSlider.minimumValue = 0
        brokeSlider.maximumValue = 1
        brokeSlider.continuous = true
        brokeSlider.tintColor = UIColor.blackColor()
        brokeSlider.value = 0
        brokeSlider.addTarget(self, action: #selector(AnnotationPhotoWidget.sliderValueDidChange(_:)),forControlEvents: .
            ValueChanged)
        self.view.addSubview(brokeSlider)
    }

    func sliderValueDidChange(sender: UISlider) {
        if sender.value <= 0.3 {
            brokeSlider.minimumTrackTintColor = UIColor.greenColor()
        } else if sender.value > 0.3 && sender.value <= 0.6 {
            brokeSlider.minimumTrackTintColor = UIColor.yellowColor()
        } else {
            brokeSlider.minimumTrackTintColor = UIColor.redColor()
        }
    }
}

@ashimVerma的解决方案效果很好。要想让它更上一层楼，获得平滑的色彩过渡，不妨给予这个：

@objc func sliderValueDidChange(sender: UISlider) {
    let saturation = 0.9 // 0...1
    let lightness = 0.46 // 0...1

    let sliderPercentage = sender.value / sender.maximumValue
    let invertedPercentage = 1 - sliderPercentage
    let hue = CGFloat(invertedPercentage * 120 / 360)

    let brightness = lightness + saturation * min(lightness, 1 - lightness)

    var adjustedSaturation: CGFloat = 0.0
    if brightness > 0 {
        adjustedSaturation = 2 * (1 - lightness / brightness)
    }

    let trackColor = UIColor(hue: hue, saturation: adjustedSaturation, brightness: brightness, alpha: 1)
    brokeSlider.minimumTrackTintColor = trackColor
}

这是通过利用HSL颜色空间来实现的，在HSL颜色空间中饱和度和亮度是恒定的。因此，我们只需要根据总色调范围的一部分来改变色调（从绿色到红色）。然后，我们将这些值转换为使用UIColor的HSB初始化器。
参考：https://en.wikipedia.org/wiki/Hue

更简单：

如果不需要在HSL颜色空间中工作，则可以通过直接设置饱和度和亮度值来进一步简化此操作。

@objc func sliderValueDidChange(sender: UISlider) {
    let sliderPercentage = sender.value / sender.maximumValue
    let invertedPercentage = 1 - sliderPercentage
    let hue = CGFloat(invertedPercentage * 120 / 360)

    let trackColor = UIColor(hue: hue, saturation: 0.95, brightness: 0.87, alpha: 1)
    brokeSlider.minimumTrackTintColor = trackColor
}