I am very new to gardening. I know these types of trees are used commonly in topiary gardening and look very nice, but I am not sure of a specific type to choose. Ideally, I would like a tree that stays dark green, grows well in clay soil with humid climate, and grows rapidly but doesn't get too humongous (like over 40 feet). Can anyone offer any ideas at all, even if they aren't exactly what I asked about? I have seen some cypress like this but they all seem to be brown colored.

Thanks,

Tasha