How to change the Green Colour in the left & top

That's not related to HikaShop but to your template. You should ask your template support such questions.

Anyway, we can't help you if you don't give the URL of your website. Each template defines CSS styles differently so we need to look at the CSS of your template to answer you.

The green background at the top is defined by:
#header ul.menu li.active a:link, #header ul.menu li.active a:visited {
color: white;
border-right: solid 1px #237D85;
background: #7BA428 !important;
}

and the green color on the left menu by:
ul.menu li a:hover, ul.menu li a:active, ul.menu li a:focus, ul.menu li.active a:hover, ul.menu li.active a:active, ul.menu li.active a:focus {
background: white url(../images/nav_level_1.gif) repeat-x;
color: #638420;
}

in the CSS file:
bandsforhim.com/templates/beez5/css/beez5.css