Ok what is your css for your menu points for these pages?
I'm sure you need to write some extra css for the underline.
This is the css you need to target the underline color of the currently active menu point.
nav.primary .current-menu-item>a span {
border-bottom-color: #fff;
}
Of course you can combine this with "body.slug-x" to make the underline white for a specific page.
http://laytheme.com/documentation.html#custom-css-styling
Thanks :)