While the color of a mural is displayed by the illumination of light, the same light may also rob it of its past radiance, not to mention that these grottoes are not isolated from the outside world.

• 壁画的颜色本来靠光的照射来显现，但光却又会夺去它昔日的鲜艳。 更何况这些洞窟不是与世隔绝的。