One clue is that a 404 page (e.g. http://color.com/asdf) says the webserver is "powered by Jetty": http://jetty.codehaus.org/jetty/

Jetty "provides an HTTP server, HTTP client, and javax.servlet container". Here is the wikipedia page for Java Servlet: http://en.wikipedia.org/wiki/Java_Servlet So the answer seems to be Java.