they can start pretty early-3 months sometimes-but really color up around 1-1.5 years old. Some lean to the green and some take on a turquoise color...and some take on a beautiful baby blue. You can usually tell which way they are going to lean by 6-10 months.
Magnets work great! Just for clarification you attach one to the branch or vine then one on the outside of the cage to connect with the one attached to the branch or vine. The metal screen may not be enough to hold the magnet without having another on the outside.