Joined: May 2006
Remember also the peppered moth, that it was whitish in the pre-industrial environment as camouflage. Fruits are more commonly camouflaged as green until they are ripe, but white also is a reasonable camouflage due to lichens, dead leaves, bleached wood, etc. (in addition to sky, dappled light, open areas that I mentioned before). White is one of the default colors in the environment, not at all a striking signal.
Some flowers are white, but they are usually, if not always, scented, and attractive to moths, not to bees and vertebrates. Hummingbirds are attracted to red flowers above all. One might ask why moth flowers are white, though, instead of green or some such color, and probably it has to do with a slight (and not costly) signal against the green leaves. In edit ,I'm adding that they may also be white in order not to be pollinated by birds and bees, but to be pollinated by the "right insects".
Do most moths see colors? I'd guess that most don't see them well in the evening, when they tend to do their pollinating. There has been a report of one insect, I believe it was a moth, that can see colors in the dark, yet I have no idea if this means that color vision is common in moths, let alone at twilight. It may not matter anyhow, since white flowers are very visible close-up (and have no pigment costs), while it is the scent that draws moths in from a distance.
White fruits are not unknown, indeed the standard warning to boy scouts, etc., is that white berries are to be considered always poisonous. Poison ivy berries are white--what eats them (of course animals are typically not affected by poison ivy--I've seen bees pollinating poison ivy, making me wonder what sort of honey that produces)?
I just googled "white berries" and "sumac", and it turns out that poison sumac berries are also white. Redosier dogwood berries are also white, says my google, and are eaten by at least 18 species of birds, including quails. Why white? I don't really know. Maybe the white berries on redosiers contrast nicely with the red bark when the leaves fall off, or maybe the berries are "meant" not to be too striking so that the right birds find them after everything else is gone, and thus might distribute the seeds better than a more indiscriminate selection of feeders would. One thing I'm saying is that not all fruits are "vying for" maximum exposure, having evolved simply to be "visible enough" to the "right organisms".
Bioluminescence in fruit? It would be fairly expensive, and would probably appeal more to nocturnal seed eaters than to diurnal birds. Fruit bats in the tropics might be signaled by bioluminescence, but as I understand it they already have a keen sense of smell and further signals would cost more than they were worth, probably. Bioluminescence evolving now would probably just attract unwanted feeders.
Nothing in biology makes sense except in the light of coincidence---ID philosophy