A door that opens when a certain team has no players/dead. Any help?

Getting the players

First, you would need to check how many players there are on that team. To do this, we'll get a table of all the players, then go through and check the teams of all of them:

local BluePlayers=0

function GetAmountOnBlue()
    BluePlayers=0
    local Players=game.Players:GetChildren()
    for _,Player in pairs(Players) do
        if Player.TeamColor==BrickColor.new("Bright blue") then
            BluePlayers=BluePlayers+1
        end
    end
end

while script.Parent do
    GetAmountOnBlue()
end

Now, this would work to constantly update the amount of players on the blue team.

Opening the door

However we still need to change the brick. To do that, we'll add in this bit of code:

if BluePlayers==0 then
    script.Parent.Transparency=1
    script.Parent.CanCollide=false
else
    script.Parent.Transparency=0
    script.Parent.CanCollide=true
end

This would check if there is any players on the 'Bright blue' team, and if there isn't, it will "open" the door.

Final product

Now that that's done, let's put the entire code together:

local BluePlayers=0

function GetAmountOnBlue()
    BluePlayers=0
    local Players=game.Players:GetChildren()
    for _,Player in pairs(Players) do
        if Player.TeamColor==BrickColor.new("Bright blue") then
            BluePlayers=BluePlayers+1
        end
    end
end

while script.Parent do
    wait()
    GetAmountOnBlue()
    if BluePlayers==0 then
        script.Parent.Transparency=1
        script.Parent.CanCollide=false
    else
        script.Parent.Transparency=0
        script.Parent.CanCollide=true
    end
end

So, I believe this should work now how you wanted.

Anyways, if you have any further questions/problems, please leave a comment below. Hope I helped :P

-Dyler3