The distances from slits 1 and 3 will differ by two wavelengths, from slits 1 and 4 by three wavelengths, and so on. The light from every slit will interfere constructively with the light from every other slit provided the distance to the screen is much greater than the size of the grating. Multiple slits of identical spacings produce an interference pattern in which the light is concentrated in fewer, brighter, narrower lines. For complete cancellation, the amplitudes of each part of the wave must be identical. If the amplitudes are not the same, then partial cancellation results.
Diffraction is the principle by which peacocks and hummingbirds display their colors.
The ridges in the surface layers of the feathers act as diffraction gratings. Interference colors result from double reflections from the upper and lower surfaces of the thin transparent coating on the butterfly wings. Some other butterfly wings produce colors by diffraction, where ridges in the surface act as diffraction gratings. The optical paths of light from upper and lower reflecting surfaces change with different viewing positions. Thus, different colors can be seen by holding the shell at different angles.