Team Change script will not work?

Error: 17:44:15.902 - Players.Player.PlayerGui.ScreenGui.Frame.TextButton.Inmates:17: attempt to perform arithmetic on a string value

Script:

player = game.Players.LocalPlayer

function getCountOfPlayersOnTeam(teamBrickColor)
local people = game.Players:GetPlayers()
local a = 0
for i = 1,#people do
if people[i].TeamColor == BrickColor.new(teamBrickColor) then
a = a + 1
end
end
return a
end

team = game.Teams.Police
function onButtonClicked()
    if getCountOfPlayersOnTeam("Deep blue") < 7 then
        player.TeamColor = BrickColor.new("Deep blue")
    else
        script.Parent.Text = "Team Full"
        wait(5)
        script.Parent.Text = "Police"
    end
end

script.Parent.MouseButton1Down:connect(onButtonClicked)