Magento, different background color for group of rows on backend grid

Question

On a backend admin page with a grid I need to change the background color for groups of rows. Not alternate color row by row as default but coloring groups according to a kn

Answer 1

The answers above are good, but sometimes you want to do the same thing without creating a new file.
Here is another way to achieve the same result remaining in the grid file.

$this->addColumn('collision_type', array(
      'header'  => $helper->__('Collision'),
      'align'   => 'center',
      'index'   => 'collision_type',
      'type'    => 'action',
      'frame_callback' => [$this, '_formatCell']
));

then in the same file

public function _formatCell($value, Varien_Object $row, Mage_Adminhtml_Block_Widget_Grid_Column $column)
{
    $value =  $row->getData($column->getIndex());
    return '
'.$value.'
';
}