To change the color of menu items, you need to navigate to Theme Options > Header and scroll down to Main menu options. First off you’ll have the settings for the 1st level menu, shown on the image below:
The same set of options is available for 2nd and 3rd level menus.
Please note that options for 1st, 2nd and 3rd menu level settings may look different on your theme
After you finished customizing your menu items, just save the changes and review your menu.
On some themes, you may have to change the color of menu items from page settings as well.
If you want to have a predefined menu item color for all your pages, you can navigate to Theme Options > Header > Header Skin and choose whether you want to use a Light or a Dark header skin:
You also need to define your menu colors. Settings for this are, in some themes, located in Theme Options > Fonts and in others, in Theme Options > Header (like is described above).
If you chose the Light skin variant, the menu text will now always be white, and your custom menu colors set in Theme Options will not take effect. Likewise, the Dark header skin will always have black menu text.
It’s also important to check the settings for your individual pages, by navigating to Page Options, under Theme Header, and check if the settings are the same as the global Theme Options. This is crucial as page settings override the settings from Theme Options, which effectively gives you the opportunity to achieve a different look and feel for the header on separate pages.
Feel free to check this article about customization of WordPress website colors, too.