system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What makes a cloud a very bright white or turn gray?

I was just looking up at the sky and I saw 2 big fluffy clouds right next to each other. One was a very bright white and the one right next to it was a solid grey color. What makes the difference in color? Please ELI5 cause my English is not that good. Thanks a lot.
gpt
Very simple. If you take a ball of cotton and pull it apart a little, it will let through alot more light. If you hold it in front of a light, you will see it appears very white. But if you put it in your hand and squeeze it together, it will be much more compact. This means that less light is let through, and it will appear much darker.