Because you did not use "reply" feature, instead create a new topic and you did not specify which applet(topic) you were talking about?  Is it  [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=39.0]Colors (Mixing color or paint: R/G/B)[/url]?

And please explain it in more detail what do you mean by "User chooses color then program gives the value"?
User chooses color from where? Inside the java applet? Or somewhere else? If it is not within the java applet region, there is no way java can read it's value.