in the default css, you have the base color defaulting to white:
body, h1, h2, h3, h4, h5, h6, p, #cssmw, dl, dt, dd, form, input {
color: #ffffff;
}
you can change the base color there, or edit the following selector:
.contentBox .productResultsWrapper .description {
margin-bottom: 5px;
min-height: 25px;
}
to change only the description.
you can use firebug:
http://www.webassist.com/tutorials/Using-Firebug
to inspect elements on your page and find CSS that is effecting them, that is what I am using to find these for you.