How do I get custom fields in views-view-unformatted-tpl.php for custom style output?

Hi,
first, thank you for that nice drupal theme.

I'm stuck for two days now on a supposingly really common use case.

I've created a view (see att. picture below) and I need to add a css-class to each row containing the content of one field that isn't displayed (goal: display a certain background image depending on that field content).

What I have tried: I've picked up "views-view-unformatted.tpl.php" renamed it to "views-view-unformatted_VIEWNAME.tpl.php" --> works.

But the data I get in there is only a "flattened" $rows object that contains only the string of the output. What I need is an associative array with all fields to receive the data I need.

The same problem i get with "HOOK_preprocess_views_view()".

How can I acheive my goal?

Any help would be appreciated!

Thanks in advance,
Mathis