Get lighter and darker color variations for a given UIColor

Question

How to get different lighter and darker variations of a given UIColor in Swift?

Answer 1

Kenji-Tran's answer works fine, as long as your starting color is not black (brightness value 0). With the addition of a few lines of extra code, you can also make black "lighter" (i.e. brighten it to a grayscale or color value).

Note: I wasn't able to add this change using an Edit and I'm not allowed to comment on Kenji-Tran's answer due to my "new boy" rep, therefore I found no other way to share my knowledge on SO then by posting a new answer. I hope that's okay.

extension UIColor {
  /**
   Create a ligher color
   */
  func lighter(by percentage: CGFloat = 30.0) -> UIColor {
    return self.adjustBrightness(by: abs(percentage))
  }

  /**
   Create a darker color
   */
  func darker(by percentage: CGFloat = 30.0) -> UIColor {
    return self.adjustBrightness(by: -abs(percentage))
  }

  /**
   Try to increase brightness or decrease saturation
   */
  func adjustBrightness(by percentage: CGFloat = 30.0) -> UIColor {
    var h: CGFloat = 0, s: CGFloat = 0, b: CGFloat = 0, a: CGFloat = 0
    if self.getHue(&h, saturation: &s, brightness: &b, alpha: &a) {
      if b < 1.0 {
        /**
         Below is the new part, which makes the code work with black as well as colors
        */
        let newB: CGFloat
        if b == 0.0 {
            newB = max(min(b + percentage/100, 1.0), 0.0)
        } else {
            newB = max(min(b + (percentage/100.0)*b, 1.0), 0,0)
        }
        return UIColor(hue: h, saturation: s, brightness: newB, alpha: a)
      } else {
        let newS: CGFloat = min(max(s - (percentage/100.0)*s, 0.0), 1.0)
        return UIColor(hue: h, saturation: newS, brightness: b, alpha: a)
      }
    }
    return self
  }
}