Selecting players on a team?

If you want to create a list of players with a certain TeamColor, iterate through game.Players:GetPlayers() and check if the player has the specified TeamColor.

If the TeamColor of the team is called "Bright blue" then you can write this:

local blue={}
for _,v in pairs(game.Players:GetPlayers())do
    if v.TeamColor.Name=="Bright blue"then
        blue[#blue+1]=v
    end
end

which will create a table blue of players on the Bright blue team.

edit: the face object is a decal inside the character's head, so to change its Texture for each player on the team, you can index the face and set the texture:

local bluetextureid="rbxassetid://########" -- image id
game.Players.PlayerAdded:connect(function(player)
    player.CharacterAdded:connect(function(character)
        if player.TeamColor.Name=="Bright blue" then
            local face=character:WaitForChild("Head"):WaitForChild("face")
            face.Texture=bluetextureid
        end
    end
end

edit: changed to run on CharacterAdded rather than one-time