Un-highlight Blog Menu Item when Category Menu Item is Selected

From what can see on your website, the Blog page is highlighted in a same way as a Podcast page because it has a class ‘current_page_parent’ that has the same styling in CSS as a ‘current-menu-item’ which is used on a Podcast menu item.

This means that the Podcast page is a child page of a Blog page. So there are two possible solutions for your problem in this case.

Solution 1.

Make the Podcast page a stand-alone (not child) page. Then this class will disappear with unwanted styling.

Solution 2.

If changing page hierarchy is not an option, add this CSS using a child theme, or Custom CSS plugin (like this one):

.header.white .topnav li.current_page_parent > a {
    opacity: 0.75 !important;
    font-family: Raleway;
    font-weight: normal;
}

This will revert the styles applied to that menu item.

Update 10/26/2016

As per your follow-up question, the snippet will look like this:

.category-podcast .header.white .topnav li.current_page_parent>a {
    opacity: 0.75 !important;
    font-family: Raleway;
    font-weight: normal;
}

Now it will work only on a podcast category archive.