custom domains x instances x workspaces

Hi and , how are you doing guys ? Let me ask you about custom domain... this feature is related to be set in 'Instance Level' and not 'Workspace Level', correct ? I am asking this because if not, would be great have this feature at workspace level too.
For example 3 workspaces for complete different projects:
RED APP (workspace #1),
BLUE APP (workspace #2),
GREEN APP (workspace #3)

if I set https://xzxz-xzxzx-xzxz.z7.redapp.io/
I will be using this 'RED APP' link for 'blue app' and 'green app' 🤕

or set another 'general app name' GRAY 😜 :
https://xzxz-xzxzx-xzxz.z7.grayapp.io/
for 'red app', 'blue app' and 'green app'.

'wished scenario' 🙏 :
https://xzxz-xzxzx-xzxz.z7.redapp.io/ <--> (workspace #1)
https://xzxz-xzxzx-xzxz.z7.blueapp.io/ <--> (workspace #2)
https://xzxz-xzxzx-xzxz.z7.greenapp.io/ <--> (workspace #3)

Is that possible or will be in the roadmap 🚗. ? ( I'm sorry 🙈 if it's possible and something from the manuals and sets I don't understand how it works )