Use this:

.aspcalendarday a {
  color: #FFF !important;
}

.aspcalendarweekendday a{
   color: #fc0000 !important;
}

.aspcalendarselectedday a{
    color: #000000 !important;
}

.aspcalendartoday a{
   color: #cc0000 !important;
}

.aspcalendarothermonth a{
   color: #660000 !important;
}

I just chose some random colors so you will need to adjust to whatever you want them to be. The key is the !important.

HTH,
Joe D.

The !important always works because it overrides all styles, no matter where they are in the order of application.

Try touching the web.config (open and save it) to clear the server cache and then refresh the site in your browser. While working on any type of skinning, it is best to have these items set to false in your web.config (or user.config).

<add key="CacheCssOnServer" value="false" />
<add key="CacheCssInBrowser" value="false" />

HTH,
Joe D.