Why do understorey Licuala palm fruits turn from red to white and then black when ripe?

Licuala ferruginea Becc., a tropical forest understorey palm, is observed
to have fruits that appear red in colour when unripe, turning
pink, then white, purple and finally black in colour as they
ripen. We monitored 13 fruiting palms in rainforest fragments and recorded
the consumption of fruits by animals via camera traps. We also
documented the fruiting phenology of two palms in the nursery. In
the rainforest fragments, a Cream-vented Bulbul (Pycnonotus simplex) was
observed plucking a mature purple fruit from a L. ferruginea
palm, before flying away with the fruit in its beak. This was the
only bird that was observed feeding on the mature fruit. A range
of mammals, dominated by edge species such as the Long-tailed
Macaque and Wild Boar, were observed to consume L. ferruginea
fruits indiscriminately across all five colour stages,
thereby limiting the dispersal of the fruits. Forest bulbul gape
sizes also matched the fruit size, suggesting that forest bulbuls
are the likely dispersers of the palm in the original forest
where edge species are not in high densities. We further posit
that the initial phase of red fruits, with high contrasting red
reflectance against a green foliage background, might be a form
of early advertisement to birds. The fruit then turns pink and
white, which have high green reflectance and is less contrasting, thereby
reducing the conspicuity of the fruit. This allows the fruit to
ripen with high fructose and glucose content, and turn purple and
black, which are known visual cues for birds. This study provides
indicative support for the dispersal syndrome hypothesis and
highlights the potential effects of forest fragmentation on
plant-frugivore interactions.