达芬奇看树叶很仔细，看光影，树有四种“偶然色彩”（accidental colors）：明、暗、光、透（shadow, light, lustre and transparency）。所谓“偶然”，既是瞬间的感觉，也可能是一种错觉。有的工具书解释Accidental color为 a false or spurious color seenin some instances, owing to the persistence of the luminous impression upon theretina。在绘画技术上，则是色彩的“漫不经心的混合”（by mixing on a painting's surface without conscious preliminary planning during the process of painting），有点儿像中国画的水墨了。他特别指出了，人-树-日的不同位置关系，会产生不同的光影效果：

The trees in landscape which are between you and the sun are far more beautiful than those which have you between the sun and themselves, and this is so because those which are in the same direction as the sun show their leaves transparent towards their extremities and the parts thatare not transparent, that is at the tips, are shining; and the shadows aredark...

他还看树叶的“风影”：

If you are on the side whence the wind is blowing you will see the trees looking much lighter than you would see them on the othersides; and this is due to the fact that the wind turns up the reverse side ofthe leaves which in all trees is much whiter than the upper side.

   有很多“像艺术家一样思考”的成功励志书（如Betty Edwards的Drawing on the Right Side ofthe Brain），我倒是觉得应该先学着像艺术家一样观察。像这儿看到的，几何的，光学的，运动的，各路神经都要活起来。遗憾的是，达翁没有风景画，只把风景做人物画的背景，我没见过他画的森林和树叶。