Very few plants flower under the shade of trees and shrubs in late summer/early autumn. On the whole shade tolerant plants are woodlanders that bloom in spring before the leaves darken the canopy.
 Even so there is colour to be found (I mean besides the colour green). Our native Arum maculatum and its relative Arum italicum both put up a spike of orange/red berries at this time of year.
 I saw these in a shady border at the South London Botanical Institute last week; not sure which Arum they are as the leaves have faded by now. Of course not all berries are edible. Succulent as they look Arums are a poisonous plant.