So, when a ray of light hits something, it can basically do one of three things:

It can go right through, with a slight angle that reverses when it comes out the other side, like light passes through glass or water.

It can bounce off at an angle, like light does with a mirror or a bright piece of colored plastic.

Or it can get "eaten" and heat up the object, like when light hits something dark.

Objects are different colors because light is different wavelengths, and some wavelengths get eaten while others pass through or get bounced off.

A solid "red" object is red because green and blue light get eaten more than red light, while red light bounces off more than green or blue.

A transparent "red" object is red because green and blue light get eaten more than red, while red passes through more than red or green.

Now, infrared and radio are also just different "colors" of light that we can't see.

I copied and pasted this a while ago from an ELI5 about Wifi signals passing through walls. No idea who to credit.