Here's a quick workaround
a { text-decoration: none; color:yourcolorhere; }
a:visited { color:yourcolorforwhenthelinkhasalreadybeenviewed; }
a:hover {color:hovercolor;}
a:acitve {color:yourlinksclickeddowncolor;}
Also if you want fancy Links for specific links use this
a[href*="yoursitedomain"]
{ color:special-color-foryour-domainname-in-posts}
What this selector does is it can be used to highlight your own domain name in a special way throughout your site so it stands out more. The *denotes the names attribute to find it on the site. Anything with yoursitedomain in it will be highlighted a different color.
As far as SEO, CSS doesn't effect it. If you have multiple sitemaps, that confuse crawlers then your SEO will be bad. Just don't hide your links, or have the display:none attribute. Certain crawlers can't view them, and make sure your robots.txt file is edited for even more SEO.
Hope this helps.