Certainly. The first thing I would recommend is trying out the Custom Colors tool which will change the entire color scheme. Here's more info:
http://en.support.wordpress.com/custom-design/custom-colors/
If you want to change just the menu colors, try adding this to your Appearance → Custom Design → CSS editor to change menu colors in the Comet theme:
/* Border color for menu and columns. */
.menu {
border-color: #91ffc5;
}
/* Background color for all menu items. */
.menu li:hover > a,
.menu li ul li a,
.menu li.current-menu-ancestor a,
.menu li.current_page_ancestor a {
background-color: #e6fff2;
}
/* Background color for selected item in the menu. */
.menu li.current-menu-item > a,
.menu li.current-menu-item > a:hover,
.menu li.current_page_item > a,
.menu li.current_page_item > a:hover {
background: #91ffc5;
}
You can change out the color codes with new ones if you'd like.
http://0to255.com/