Whenever we have a "macro" object like a buckyball, it has many electrons and quarks if not something more fundamental, all of which have their own wavefunctions that interact with each other. But in the double-slit experiment, we show that the minimas and maximas occure for only photons/electrons with a single wavelength. If we take a combination of wavelengths, like visible light, we won't have a distinct interference pattern. (although we do see some separation at the edges of bright intensity bands)
Then, how is it possible that something that is a combination of various matter waves with different wavelengths like a buckyball, also shows the same kind of interference pattern?