I noticed it on my 2020 3500 as well. Mine fades on as I dim the interior lights at night. It's at the dealer now for that and a couple other issues. They gave me a 1500 loaner and it does it as well. I don't think it's supposed to do that. It seems like a design flaw.
Just picked up my new 2020 3500 LT crew cab gasser in Northsky Blue yesterday. There aren't a lot of blue ones on this thread and there needs to be more.
I traded in a 2015 1500 in Rainforest Green with 121k on it. The upgrade is for pulling a travel trailer that beat up my trans and suspension pretty bad.