Hiya - I want to change the colour of the grey stripes so they are the same as the background colour of my menus - so I'd have 2 stripes of orange rather than grey (http://www.lactivist.net)

Huge thanks
Lisa

Those gray stripes are a background image. You will have to create a new one to replace what is there. The image is called in ATO>Body, Text, & Links as:

background: #fff url('<?php bloginfo('template_directory'); ?>/images/background7.png') repeat-x top left;

cool, thank you! there is still a chunk missing though, should I do backgrounds 5 and 6 as well?

I'm not sure what you mean by there is a chunk missing but it shouldn't have anything to do with the other images. You just need to remove that background line in ATO>Body, Text, & Links. You also may want to go to ATO>Add HTML/CSS Inserts>CSS Inserts and take out the background line.
Change This

div#menu1 ul.rMenu {
background: transparent;
border: none;
}

To This

div#menu1 ul.rMenu {
border: none;
}

The bit missing is the grey section next to 'polls' that runs all the way up to and past the search box on www.lactivist.net. I tried taking off the search box but it made no difference.

Thanks, sorry to be thick but I can't see what I am supposed to do on the first bit you suggested, there seems to be no option for that, and on the css inserts there is no place to change code just this:

CSS Inserts Add CSS code here that you want to append to your theme's CSS file.

So it looks like I can add code but not take it away or change it

In ATO>Add HTML/CSS Inserts>CSS Inserts in the big box you should see a whole bunch of CSS. One of entries should start with div#menu ul.rmenu. You need to take out the background:transparent line.

Here is a video of what I mean.