code: public function allFills(Spreadsheet $spreadsheet)
      {
          // Get an array of unique fills
          $aFills = [];
  
          // Two first fills are predefined
          $fill0 = new Fill();
          $fill0->setFillType(Fill::FILL_NONE);
          $aFills[] = $fill0;
  
          $fill1 = new Fill();
          $fill1->setFillType(Fill::FILL_PATTERN_GRAY125);
          $aFills[] = $fill1;
          // The remaining fills
          $aStyles = $this->allStyles($spreadsheet);
          /** @var \PhpOffice\PhpSpreadsheet\Style\Style $style */
          foreach ($aStyles as $style) {
              if (!isset($aFills[$style->getFill()->getHashCode()])) {
                  $aFills[$style->getFill()->getHashCode()] = $style->getFill();
              }
          }
  
          return $aFills;
      }
docs: Get an array of all fills.
  
  @param Spreadsheet $spreadsheet
  
  @return Fill[] All fills in PhpSpreadsheet