$attrCode = 'color_base';

$sourceModel = Mage::getModel('catalog/product')->getResource() ->getAttribute($attrCode)->getSource();

$valuesText = explode(',', 'red,green,blue');

$valuesIds = array_map(array($sourceModel, 'getOptionId'), $valuesText);

$OptionIds = implode(',', $valuesIds);

$product->setColorBase($attrCode, $OptionIds);

$product->getResource()->saveAttribute($product, 'color_base');

$attrCode = 'color_base'; $sourceModel = Mage::getModel('catalog/product')->getResource() ->getAttribute($attrCode)->getSource(); $valuesText = explode(',', 'red,green,blue'); $valuesIds = array_map(array($sourceModel, 'getOptionId'), $valuesText); $OptionIds = implode(',', $valuesIds); $product->setColorBase($attrCode, $OptionIds); $product->getResource()->saveAttribute($product, 'color_base');