How can I change the bounce of SKSpriteNode dynamically?

I have a very simple app. All SKSpriteNodes, myBall, myBlue, and myRed.

Only myBall moves, affected by gravity, and bounces off of different objects (myRed and myBlue).

What I can't figure out is how to make myBall bounce harder or softer depending on which body it hits?

I hav been playing with the density of all the objects, but it doesn't seem to make any difference? Is there some property I am unaware of? Or are there other methods?

How can I change the bounce of SKSpriteNode dynamically?
 
 
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