I actually used to think this too, when my friend was building I had to ask her "um, why did you choose that colour for your door..?" I wonder why this is the colour doors come in.
They had one of these unpainted bright-green doors on both my front and garage doors, and when I saw it I was all "omg, that's awesome! But then I realised "wait, we picked Dune for the front door... bugger"