How do I adjust the fill layer so that it changes color based on what it overlays?

[madeliner16275940]

I have a file from a professional graphic artist where he has these color dots changing color based on what they're overlaying. They even change the color of the thing they're overlaying as well. 

I want to replicate this effect in another illustration but cannot figure out how to do so. Any help would be greatly appreciated! I'm using Illustrator 2020

[madeliner16275940 · Accepted solution]

Idk if I'm allowed to retire this post, but I believe I found that you can do this in blending mode! However, if anyone has anything to add, feel free. Thank you

[Ton Frederiks · Accepted solution]

Yes, check the blending mode in the Appearance panel.

It may be applied to the object, but it could also be applied to the layer that contains the object.