I can give you a few tips, but I cannot teach you CSS here. We sell templates and extensions, we are not a webmaster school yet. I hope you understand that.
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You can change Menu background-color by two methods:
a) Using different template Preset color, by default is blue (1) - from template options
OR
b) By using custom CSS
#sp-main-menu > .container > .row:first-child, .aspasia-nav-tabs-one .sppb-nav-tabs,
.aspasia-get-in-touch > div, .aspasia-image-with-content .sppb-content-holder::before,
.aspasia-contact-details .sppb-addon-content,
#hikashop_address_form_span_iframe form input[type="submit"]
{ background: yellow; }
How to use Custom CSS was explained in Helix3 documentation as well.