colors

i just remembered the one time i went to this program in dr. dirnbach's after school for computer design and such. i mean i only went to it because they offered free pizza, but they said something that kind of made me confused. they started to talk about the primary colors and they told me that the primary colors were red, green, and blue. something is wrong here. no matter how hard they tried i could not be convinced that green was a primary color, not in nature at least. they then went on to tell me that it's been proven by scientists. see usually i'm an extremely rational person, and when backed up with evidence i tend to start to agree with scientific fact, but this i just could not agree with. i asked them if they could tell me how to create yellow, which they never did and i asked them to tell me what backs up this scientific fact of green being primary which they also never answered. i just cannot comprehend how i would go about making yellow with paint, if there was one thing i always understood, it was the way primary colors work and to be told that something i've believed to be solid fact isn't true is a bit unsettling. yellow and blue make green, yellow and red make orange, how do you accomplish this replacing yellow with green?