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The font color of your menu items will automatically change based on the background color of your header between white and black, whichever one is more visible. If you want to use a custom color for your menu item text then you will need to use CSS to change it and the following code will allow you to supply you own color value to customize as needed.
.palette-primary .navbar-default .navbar-nav > li > a {
color: #HEXCODE;
}
Please let us know if you have any additional questions, we are always happy to help!