The colour orange occurs between red and yellow in the visible spectrum at a wavelength of about 585–620 nm, and has a hue of 30° in HSV colour space. It is numerically halfway between red and yellow in a gamma-compressed RGB colour space, the expression of which is the RGB colour wheel. The complementary colour of orange is blue. Orange pigments are largely in the ochre or cadmium families, and absorb mostly blue light. Source of course.
This is the result of my pinhole camera experiment. As you can see, the light leaked quite a bit, and I think the orange stripe effect is perhaps from the red tape that I used to construct the camera. It may be quite fun to create a blue or green one and see what happens.
It was quite hard to tell what most of the photographs were of, although I do recognise a tree from montjuic and the street corner from my terrace. Mostly they are just orange light blurs, which I suppose is sort of interesting in itself.