I have got the rotation part right. When someone joins the game, the rotation changes. But the color does not. It changes to "Dark Stone Gray". I got this answer from DevFrank... here it is,
local leaf = script.Parent
local colors = {"Pastel Green", "Bright Green", "Medium Green", "Sand Green"}
game.Players.PlayerAdded:connect(function()
leaf.CFrame = CFrame.new(leaf.CFrame.x, leaf.CFrame.y, leaf.CFrame.z) * CFrame.Angles(math.random(), math.random(), math.random())
leaf.BrickColor = BrickColor.new(colors[math.random(1, #colors)])
end)
Please find out what is wrong with the colors.

1 comment
Check your capitalization. I don't think the "G" in "green" is supposed to be capitalized in Lua.