Hey guys, I'm just trying to get my head around the RGB tristimulus graph, as follows: [URL]http://cnx.org/content/m18092/latest/trist.png[/URL] Why are there negative values for red? What does it mean? I'd appreciate it if someone could help. And no, this isn't a homework question, it's part of my Computer Graphics course notes, and I'm having trouble understanding this particular concept. Thank you!