admin cp ----> usergroup manager ------> administrators -----> first box <span style="color: red;"> 2nd box </span>

It works perfectly.

didn't work and what wierd is that i got another forum and there it's working

Some reasons it wouldn't work:
- the users are in a secondary usergroup and that markup takes precedence
- the template is modified to not use the username markup
- a modification is interferring with the markup

Check out those three things.

By looking at the screenshot, you did it wrong.

The 2nd tag is </font>, not <font/>

And get rid of the unneeded 's

Also looking at the screen shot, red doesn't have quotes on both sides of it like it should, you only have them on one side ('red instead of 'red', or more properly "red" - although even more properly is the css version posted above by the_stig).

the first one is not.
but the 2nd and the 3rd maybe
but how can i check it?
i know that it dosent suppoesd to be like that but because the system is translate to hebrew.
and from my exprince with it on other forum it's should work and i tried to like you suggest to be and it doesnt have any affect

So because it is in hebrew, you can get away with going <font color='red> instead of <font color='red'>? That is very strange and doesn't seem right, but if you say so....

As for whether it is the template, create a new style with no parent - Styles & Templates > Style Manager > Add New Style > no parent - then browse the site using that totally default vbulletin style - are the usernames correctly marked up then?

And for whether it's a modification, try disabling your plugins and see if you still have this problem.
Note: To temporarily disable the plugin system, edit config.php and add this line right under <?php