prova con

if(ismod($uid)) $addClass = " Blued";
if(!sowner(getuid_sid($sid))) $addClass = " Greened";
if(isheadadmin(getuid_sid($sid))) $addClass = " Yellowed";
if(isadmin(getuid_sid($sid))) $addClass = " Redded";

echo "<span class=\"time$addClass\">[$ds]</span><a href=\"chat.php?action=say2&sid=$sid&who=$chat[0]&rid=$rid&rpw=$rpw\"><span class=\"nickname\">$optlink</span></a> - ";
echo "<span class=\"$addClass\" style=\"color:#$colorchatmsg[0]\">".strtolower($tosay)."</span>
";

Poi definisci un CSS con le diverse classi che settano i colori.