Fixes

src/hsl.ts

@@ -11,27 +11,29 @@ export default class HSL {
         this.lightness = lightness
     }
 
-    // https://en.wikipedia.org/wiki/RGB_color_model
+    // https://en.wikipedia.org/wiki/HSL_and_HSV
     public static fromRgb(rgb: RGB) {
         const redValue = rgb.red / 255,
             greenValue = rgb.green / 255,
             blueValue = rgb.blue / 255,
-            lightness = (redValue + greenValue + blueValue) / 3,
+            max = Math.max(redValue, greenValue, blueValue),
+            min = Math.min(redValue, greenValue, blueValue),
+            chroma = max - min,
+            lightness = .5 * (max + min),
             saturation = 1 - (3 / (redValue + greenValue + blueValue)) * Math.min(redValue, greenValue, blueValue)
 
-        const dividend = (redValue - greenValue) + (redValue - blueValue)
-        const divisor = 2 * Math.sqrt((redValue - greenValue) ^ 2 + (redValue - blueValue) * (greenValue - blueValue))
-        let hue = (1 / Math.cos(dividend / divisor))
-        if (greenValue > blueValue) hue = 360 - hue
+        let huePrime = 0
+        if (chroma != 0) {
+            if (redValue == max) huePrime = ((greenValue - blueValue) / chroma) % 6
+            else if (greenValue == max) huePrime = ((blueValue - redValue) / chroma) + 2
+            else huePrime = ((redValue - greenValue) / chroma) + 4
+        }
 
-        return new HSL(hue, saturation, lightness)
+        return new HSL(huePrime * 60, saturation, lightness)
     }
 
     public static fromHex(color: number): HSL {
-        const red = color >> 16
-        const green = (color - (red << 16)) >> 8
-        const blue = color - (red << 16) - (green << 8)
-        return HSL.fromRgb(new RGB(red, green, blue))
+        return HSL.fromRgb(RGB.fromHex(color))
     }
 
     public toHex(): number {

src/rgb.ts

@@ -49,4 +49,11 @@ export default class RGB {
 
         return new RGB((red + match) * 255, (green + match) * 255, (blue + match) * 255)
     }
+
+    public static fromHex(color: number): RGB {
+        const red = color >> 16
+        const green = (color - (red << 16)) >> 8
+        const blue = color - (red << 16) - (green << 8)
+        return new RGB(red, green, blue)
+    }
 }