Hello,
I didn't think it was possible to specify individual colours for each menu item, but I've just had a quick look and have a possible solution.
This will only work for a site that you are currently coding, you will need to adapt the technique for each menu item and site that you create.
Using the Web Developers Toolbar for firefox - go to Information / Display ID & Class details
here you will be able to view all of the ids assigned to each individual Solpart menu item.
From there you can create css specifically for each item, for instance:
#tddnn_dnnMENU_ctldnnMENU99
{
background-color: pink;
}
For further info on using the web developers toolbar check out:
Troubleshooting DotNetNuke Skins