You can control this by adding or updating styles in the qa-style.css file. I guess you're using a customization of the Snow theme so you should locate these CSS selectors:
a:link, a:visited {
text-decoration: none;
color: #0179b5;
}
a:hover, a:active {
color: #0179b5;
text-decoration: underline;
}
Then you can apply the changes you want:
a:link, a:visited {
text-decoration: none;
color: red;
font-weight: bold;
}
a:hover, a:active {
text-decoration: underline;
color: red;
font-weight: bold;
}
(In this case you could also move the color and weight to a parent selector).
If the color is not turned for a given link then that link has been applied a particular style. You'll have to locate that style and perform the changes the same way. For example, for the My updates and Logout buttons in your example, you'll have to remove/change this class:
.qa-nav-user-link {
color: #3B5998 !important;
}
For the username this one:
.qa-user-link {
color: #3B5998 !important;
font-weight: 700;
}