The following works for me in both 1.5 and 1.6:
.navbar {background-color: red;}
You've got a space between your dot and 'navbar' in your post, if that's present in your CSS too, that could be the problem. Running your CSS through a validator helps to pick up these potential little troubles.
If that's not the case then make sure that you're adding your new CSS after anything else that's setting the color of the navbar, later CSS will overule earlier settings.
I'd also recommend the Web developer extension for Firefox. It can be a great help in examing the structer of web pages and its edit CSS function lets you try things out and see the results live.
Ian, you can also go to the Chameleon website and experiment with Moodle CSS settings on screen and live with the interactive Chameleon theme. When you got what you want you can copy the CSS from the editor and paste it into your CSS files.
The description how to work with Chameleon you find on the website.
I hope this helps
Urs
One thing I've found when changing style sheets, after much head-scratching and wondering why something wasn't changing when I was sure I was modifying the right style definition, is that in IE you have to clear the .css files from your cache every time before refreshing the page. I fell for it again this morning - found the font size I wanted to change, changed it, then spent ten minutes trying to work out if it was a different style after all. Loaded it into Firefox instead and it worked perfectly first time. Doh! 
Chris
