What does 的 mean in 电影展示在盲人面前的不只是一时的多彩
「的」in that context means that which is....

電影展示在盲人面前「的」不衹是一時的多彩，電影改變着每一個聽電影的盲人的人生。
That which movies exhibit to visually-impaired people are not just fleeting displays of magnificence; for those people that listen, movies change their whole life.

Compare:

紅車 (Red car)
紅「的」是車 (That which is red is the car)

Grammatically, what's being cut out here is something like 東西 or 事情. The full expression of the above example might be something like 紅的東西是車 (The red thing is the car &gt; That which is red is the car).