Writing board

I just have a question that keeps bugging me ever since our school days... Our

"black board"

..ala...papa hitam..u know what i mean.. But why do we call it black board? Yes. it is a board. But black?? I have never written on a board that is black!!
every board i had accountered was actually

"GREEN!!"
why dont we all call it green board? if we can call the white board (esp those used in form 6 classes)...white board...why a board in green called black board?? Is this a generalization of word..macam kalau diapers..instead of calling them lampin..we normally call them pampers (in Malaysia) and prima (in turkey)???

Hmm.... This is something we should think about..So if you know or want to speculate the history of why we call the green coloured board a black board..pls do..