Something

<?php
	public function replaceColor($color=null) {
		if($color === null) {
			$color = $this->imcb->black;
		}
		
		$imit = $this->im->getPixelRegionIterator(5, 5, (int)ceil($this->im->getImageWidth() * 0.15), (int)ceil($this->im->getImageHeight() * .15));
		while($row = $imit->getNextIteratorRow()) {//we're actually going to edit this one
			$rowNumber = $imit->getIteratorRow() + 5;
			echo $rowNumber.' ';
			foreach($row as $col => $pixel) {
				if($pixel->isSimilar($color, BLACK_LEVEL)) {
					if($this->im->getImagePixelColor((int)$col, (int)$rowNumber + 1)->isSimilar($pixel, BLACK_LEVEL)) {
						$pixel->setColor('purple');
						$imit->setIteratorRow($imit->getIteratorRow());
						break;
					}
				}
			}
			$imit->syncIterator();
		}
	}

?>