Fixed issue #11581:

Changed references from Zend_Pdf_Color_RGB to the correct camel case class name Zend_Pdf_Color_Rgb

Author: dverkade

app/code/Magento/Sales/Model/Order/Pdf/Creditmemo.php

@@ -75,12 +75,12 @@ public function __construct(
     protected function _drawHeader(\Zend_Pdf_Page $page)
     {
         $this->_setFontRegular($page, 10);
-        $page->setFillColor(new \Zend_Pdf_Color_RGB(0.93, 0.92, 0.92));
+        $page->setFillColor(new \Zend_Pdf_Color_Rgb(0.93, 0.92, 0.92));
         $page->setLineColor(new \Zend_Pdf_Color_GrayScale(0.5));
         $page->setLineWidth(0.5);
         $page->drawRectangle(25, $this->y, 570, $this->y - 30);
         $this->y -= 10;
-        $page->setFillColor(new \Zend_Pdf_Color_RGB(0, 0, 0));
+        $page->setFillColor(new \Zend_Pdf_Color_Rgb(0, 0, 0));
 
         //columns headers
         $lines[0][] = ['text' => __('Products'), 'feed' => 35];

app/code/Magento/Sales/Model/Order/Pdf/Invoice.php

@@ -82,12 +82,12 @@ protected function _drawHeader(\Zend_Pdf_Page $page)
     {
         /* Add table head */
         $this->_setFontRegular($page, 10);
-        $page->setFillColor(new \Zend_Pdf_Color_RGB(0.93, 0.92, 0.92));
+        $page->setFillColor(new \Zend_Pdf_Color_Rgb(0.93, 0.92, 0.92));
         $page->setLineColor(new \Zend_Pdf_Color_GrayScale(0.5));
         $page->setLineWidth(0.5);
         $page->drawRectangle(25, $this->y, 570, $this->y - 15);
         $this->y -= 10;
-        $page->setFillColor(new \Zend_Pdf_Color_RGB(0, 0, 0));
+        $page->setFillColor(new \Zend_Pdf_Color_Rgb(0, 0, 0));
 
         //columns headers
         $lines[0][] = ['text' => __('Products'), 'feed' => 35];

app/code/Magento/Sales/Model/Order/Pdf/Shipment.php

@@ -80,12 +80,12 @@ protected function _drawHeader(\Zend_Pdf_Page $page)
     {
         /* Add table head */
         $this->_setFontRegular($page, 10);
-        $page->setFillColor(new \Zend_Pdf_Color_RGB(0.93, 0.92, 0.92));
+        $page->setFillColor(new \Zend_Pdf_Color_Rgb(0.93, 0.92, 0.92));
         $page->setLineColor(new \Zend_Pdf_Color_GrayScale(0.5));
         $page->setLineWidth(0.5);
         $page->drawRectangle(25, $this->y, 570, $this->y - 15);
         $this->y -= 10;
-        $page->setFillColor(new \Zend_Pdf_Color_RGB(0, 0, 0));
+        $page->setFillColor(new \Zend_Pdf_Color_Rgb(0, 0, 0));
 
         //columns headers
         $lines[0][] = ['text' => __('Products'), 'feed' => 100];