This is a simple magento tips but there are many people have asked for.

You can find and edit this file:

magento\app\code\core\Mage\Catalog\Model\Product\Image.php

find this code:

protected $_backgroundColor  = array(255, 255, 255); //white background

change the background to the color you prefer:

protected $_backgroundColor  = array(0, 0, 0); //black color

//protected $_backgroundColor  = array(0, 0, 255); //blue color

Clear cache and refesh the fontend to get your result.

Good work!

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