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。