Overrides theme_tablesort_indicator().
Uses Seven's image versions, so the arrows show up as black and not gray on gray.
function seven_tablesort_indicator($variables) {
$theme_path = drupal_get_path('theme', 'seven');
if ($variables['style'] == 'asc') {
$image_uri = $theme_path . '/images/arrow-asc.png';
$text = t('sort ascending');
}
else {
$image_uri = $theme_path . '/images/arrow-desc.png';
$text = t('sort descending');
}
$image = array(
'#theme' => 'image',
'#uri' => $image_uri,
'#alt' => $text,
'#width' => 13,
'#height' => 13,
'#title' => $text,
);
return drupal_render($image);
}