Reapply "Allow alpha in RGBA strings"

This reverts commit 4360517.

Author: vmcj

webapp/src/Utils/Utils.php

@@ -371,11 +371,15 @@ public static function componentToHex(int $component): string
     /**
      * Convert an RGB triple into a CSS hex color.
      *
-     * @param array{int, int, int} $color
+     * @param array{int, int, int}|array{int, int, int, int}  $color
      */
     public static function rgbToHex(array $color): string
     {
-        return "#" . static::componentToHex($color[0]) . static::componentToHex($color[1]) . static::componentToHex($color[2]);
+        $result = '#';
+        for (int i = 0; i<count($color); i++) {
+            $result += static::componentToHex($color[$i]);
+        }
+        return $result;
     }
 
     public static function relativeLuminance(string $rgb): float

webapp/tests/Unit/Utils/UtilsTest.php

@@ -341,6 +341,8 @@ public function testRgbToHex(): void
         self::assertEquals('#000000', Utils::rgbToHex([0, 0, 0]));
         self::assertEquals('#abcdef', Utils::rgbToHex([171, 205, 239]));
         self::assertEquals('#fedcba', Utils::rgbToHex([254, 220, 186]));
+        self::assertEquals('#fedcbaff', Utils::rgbToHex([254, 220, 186, 255]));
+        self::assertEquals('#fedcba00', Utils::rgbToHex([254, 220, 186, 0]));
     }
 
     public function testRelativeLuminance(): void