Single slit diffraction at the central bright fringe Why is the color white at the centeral bright fringe when a white(polychromatic) light passes through a small aperture
 A: In diffraction and interference experiments with the white light. Central fringe is white because all wavelength has same path difference on optical axis goes through the center of the system of apertures.
But as you go far from the center axis, optical path difference varies for different wavelength and different color get separated.


A: I have yet to see such a thing happening.
Monochromatic means light of one wavelength and so all the fringes will be of the same colour.
The only reason why the central maximum might appear to be of a different colour from the rest of the fringes is if you are looking at the interference pattern directly with the eye or a camera and the intensity of the central fringe is so great as to completely overwhelm the receptors of light on the cornea/ccd screen.  

Because of the enormous contrast between the central maximum and the subsidiary maxima it is very difficult to photograph such interference patterns because if one part the exposure is correct another part will be grossly under/over exposed.
