OT: Question about RGB color method

[John Salerno]

Sorry for this non-Python question, but since it's computer related I 
know you guys will have an answer, and I don't really know where else to 
ask. Mainly I'm just curious anyway.

I'm wondering, why do computers use a RGB color scheme instead of the 
primary colors? Is there something you can't do with yellow? It seems 
weird that RGB can be combined to make all colors, when that's supposed 
to be the job of the primary colors. I'm sure there some technical 
computer-related reason that it had to be this way.

Thanks.