Besides a new home for Ambiant-MATE, it is officially a community effort to keep maintained.
While the colours won't be conveniently installable via Welcome 22.04 onwards - the colours are still there via that PPA:
ambiant-mate-colours-aqua
-blue
-brown
-orange
-pink
-purple
-red
-teal
-yellow
If anyone wants to know more, here's information about the situation from the previously named ubuntu-mate-colours
project: