In the reference photo, the bright sunlight on the pale colored leaves has caused the camera lens to close down, making the trunks appear darker than the actually are. My objective in this drawing is to attempt to capture the bright white which Aspen bark has in nature, while maintaining the brilliant fall colors of its leaves in direct sunlight.
For this particular drawing, that becomes a balancing act to keep both trunks and leaves bright, without allowing the drawing to become too light and appearing washed-out.
At this point, it appears we need more contrast between leaves and trunks, so I will now go back and darken larger areas of the leaves with the same colors used previously, to provide that extra depth and balance.
Later, after I have completed the trunks, I will evaluate the overall drawing again to determine if an even darker color should be added to portions of the leaves.