         self.a = a
         self.b = b
     }
-    public init(lightness: Double, saturation: Double, hue: Double) {
+    public init(lightness: Double, chroma: Double, hue: Double) {
         self.lightness = lightness
-        self.a = saturation * cos(2 * M_PI * hue)
-        self.b = saturation * sin(2 * M_PI * hue)
+        self.a = chroma * cos(2 * M_PI * hue)
+        self.b = chroma * sin(2 * M_PI * hue)
     }
 }
 

            return positive_mod(0.5 * atan2(b, a) / M_PI, 1)
        }
        set {
            self = LabColorModel(lightness: lightness, saturation: saturation, hue: newValue)
        }
    }
    
    public var saturation: Double {
        get {
            return sqrt(a * a + b * b)
        }
        set {
            self = LabColorModel(lightness: lightness, saturation: newValue, hue: hue)
        }
    }
}

            return positive_mod(0.5 * atan2(v, u) / M_PI, 1)
        }
        set {
            self = LuvColorModel(lightness: lightness, chroma: chroma, hue: newValue)
        }
    }
    
    public var chroma: Double {
        get {
            return sqrt(u * u + v * v)
        }
        set {
            self = LuvColorModel(lightness: lightness, chroma: newValue, hue: hue)
        }
    }
}
