I used this idea from a great blog, Being LDS.
We started with a white flower and clear water.
I dropped red food coloring in to the water to represent our sins that Christ would take upon himself.
When we came to class the next morning, the white flower was red.
It had taken on all the sins, pain, sorrow, hurts, of the world.
Very effective visual to teach the Atonement.
It was interesting to hear my students come to the realization that they could give more than their sins to Christ and that he would take their pain, sorrow, disappointment, hurt, etc.