Isn't that "cogito, ergo sum" thingy a good enough answer? Geez!

In fact, rain water is colorless.

But why does it appears as raindrops in our eyes? Because it possesses the same power as yours.

That's right! I wonder what I was dreaming about...

If I take away refracted light coming from the raindrops, the rain will be invisible.

This way, humans will be tricked that the rain has stoped, and they'll come out.

Umm... 40 points. There is another thing that comes out after the rain, right?

You're strict...

If we don't prepare "that thing" only your proud light refraction ability can create...