Solution for this topic

It seems from your shared screenshot that the About us menu item is second menu item in the menu so you can change its color by adding the following CSS code in the Custom CSS code option of your theme on the below path.

Admin Area -> Appearance -> Theme Settings -> Custom Code -> CSS Code

.sh-nav > li.menu-item:nth-child(2) > a {
    color: #000;
}

You can change the color value in the above code to whatever you want to use by referring the following pages.

http://www.w3schools.com/html/html_colors.asp
http://www.w3schools.com/html/html_colorvalues.asp
http://www.w3schools.com/tags/ref_colorpicker.asp