Please go to My Site → Customize → CSS (or Additional CSS), then add all of the following code to the bottom of that window.
/* This CSS changes the site title color.
* 10735834-hc (jw)
*/
.site-title a {
color: #ffffff;
}
.site-description:before {
border-top: 1px solid #ffffff;
border-bottom: 2px solid #ffffff;
}
Tip: keep the /*
comment */
in the code to later know what this code does.