diff --git a/.circleci/config.yml b/.circleci/config.yml
index dc51d3d..4770cf1 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -48,4 +48,4 @@ workflows:
       - unittest:
           matrix:
             parameters:
-              php-version: ["8.1", "8.0"]
+              php-version: ["8.1", "8.0", "5.6"]
diff --git a/src/BaseColor.php b/src/BaseColor.php
index feed072..c0e931d 100644
--- a/src/BaseColor.php
+++ b/src/BaseColor.php
@@ -4,17 +4,17 @@
 class BaseColor
 {
     const COLOR_ROUNDING_COEFF = 0x33;
-    private $r;
-    private $g;
-    private $b;
-    private $a;
+    public $r;
+    public $g;
+    public $b;
+    public $a;
 
     function __construct($r = null, $g = null, $b = null, $a = null)
     {
-        $this->r = $r ?? 0;
-        $this->g = $g ?? 0;
-        $this->b = $b ?? 0;
-        $this->a = $a ?? 0;
+        $this->r = $r ? $r : 0;
+        $this->g = $g ? $g : 0;
+        $this->b = $b ? $b : 0;
+        $this->a = $a ? $a : 0;
     }
 
     function getClone()
@@ -58,7 +58,7 @@ function toArray()
         ];
     }
 
-    function toString()
+    protected function toString()
     {
         return join(',', $this->toArray());
     }
@@ -94,12 +94,7 @@ function toGd($image, $toAlpha = null)
                 $this->a
             );
         } else {
-            return imagecolorallocate(
-                $oGd,
-                $this->r,
-                $this->g,
-                $this->b
-            );
+            return imagecolorallocate($oGd, $this->r, $this->g, $this->b);
         }
     }
 }