It’s a feature on #[2] TestFlight.
Colors indicate the % of your donation amount to support development. Cyan for the lowest to yellow for 100%. 
Discussion
Where to set this up? I cannot find it🤦🏼♂️
If you’re on the latest build it’s the Wallet option in your profile menu. 
Does this just works with alby?
For now I think so, other wallets have to enable the feature. Someone is working on a self-hosted method.
I cannot use alby yet. I am testing so many things rn just to get more confident with bitcoin in general and to get a better understanding. It’s to many informations for me at the moment.