(not urgent) Can someone help me understand lists?

I have been using Scratch for a while and I decided to try out App Inventor. I love it, it is so much faster than Scratch at doing things, yet I am having a little bit of trouble understanding lists. Some lists are blocks that can go inside and input to other blocks
image like this but others just go into the code like this
image and I was wondering how I use these blocks since they cant go into a block. How can I use these modifiers for a list? They seem to be different from Scratch, where in Scratch the only option was the latter block, yet you could use a list block as an input, it's hard to explain. Anyway i was wondering how I can get the output of the "replace list item" block and use it? Here is my code, I want to randomize a color value. Here are my blocks, and I also just want to understand lists in general as well.

Try this tutorial List Blocks On App Inventor | imagnity

One option is to use again the GetPixelColor method after changing the color

Taifun

More than you ever wanted to know about AI2 lists