Any ideas on how to edit colours?

I can see a very thin grey line surrounding your slider and navigation, is that what you mean?

In the css, I can see this –

#header #mainmenu {
float: left;
border: 1px solid #CCC;
background-color: white;
margin-top: 40px;
position: relative;
width: 976px;
z-index: 1000;
box-shadow: 0 1px 0px white;
}

The grey you are seeing is the border: 1px solid #CCC;

You could make a child theme and change the colour in there.

Hi, not sure if we’re talking about the same thing. It’s not very thin. It’s huge and it’s a very light grey colour slightly different to the white. Armchair boxing is written upon it. It circles the entire slider.

That grey is an image set in this CSS code:

#header {
    background: url("images/header-bg.jpg") repeat-x scroll left bottom transparent;
    padding-bottom: 20px;
}

As noted by Christine, you should use a custom CSS option or plug-in to make changes or a child theme, or they will be erased when you update the theme.

Then add this to your CSS:

#header {
    background: #FFFFFF;
}

You should also have a look at firebug. It’s a great way to figure out what CSS does what in your theme.
Here’s a tutorial that you may find interesting:
– https://www.studiopress.com/tips/using-firebug.htm