Have you tried using Kobo Desktop to look at the book?
I download a preview of "The Illuminatus! Trilogy The Eye in the Pyramid, The Golden Apple, Leviathan" via Kobo Desktop and WiFi to my Glo and saw that the Table Of Contents was in a lighter shade of gray.
Viewing the book via Kobo Desktop, the TOC is BLUE.
Looking at the kepub file (previews are not encrypyed, and can be copied to have either a .epub or .zip extension) the TOC is styled with an inline style of
Code:
<style xmlns="http://www.w3.org/1999/xhtml" type="text/css" id="kobostylehacks">
div#book-inner p, div#book-inner div {
font-size: 1.0em; }
a {
color: black; }
a:link, a:visited, a:hover, a:active {
color: blue; }
div#book-inner * {
margin-top: 0 !important;
margin-bottom: 0 !important;}
</style>
So I think it's safe to say it's related to the colour applied to the text via CSS.