Hi Mark,
As I can see that the header is sticky now when scrolling the page on your site, did you get it solved?
To change the background of the header on scroll, you can override this css rule:
.not-at-top #t4-header.t4-sticky {
background-color: #fff !important;
}
and for the menu item color:
.not-at-top #t4-header.t4-sticky .t4-megamenu .navbar-nav>li>a,
.not-at-top #t4-header.t4-sticky .t4-megamenu .navbar-nav>li>.nav-link {
color: var(--mainnav-link-color);
}
/*on hover*/
.not-at-top #t4-header.t4-sticky .t4-megamenu .navbar-nav>li>a:hover,
.not-at-top #t4-header.t4-sticky .t4-megamenu .navbar-nav>li>a:focus,
.not-at-top #t4-header.t4-sticky .t4-megamenu .navbar-nav>li>a:active,
.not-at-top #t4-header.t4-sticky .t4-megamenu .navbar-nav>li>.nav-link:hover,
.not-at-top #t4-header.t4-sticky .t4-megamenu .navbar-nav>li>.nav-link:focus,
.not-at-top #t4-header.t4-sticky .t4-megamenu .navbar-nav>li>.nav-link:active {
color: var(--mainnav-link-hover-color);
}
and change to your desired color.