Why wont the Gui come up?

So I need Blood to go on your screen if your health is 50 or smaller or equal to but if your health is equal to or higher then 70 its not. Pretty simple I would think but it wont work. This script is inside the Gui and its a normal script not local. Also this same script is in two other Gui's but the 50 and 70 are changed, basically it makes it so the more hurt you are, the more blood comes up. Heres the script:

player = script.Parent.Parent.Parent.Workspace.Character
person = player.Humanoid
while true do
if person.Health >= 70 then
	script.Parent.Visible = true
end
if person.Health <= 50 then
	script.Parent.Visible = false
end
wait()
end

Help please I thought this would work.

Heres the proper script :

(Make this inside starterpack,Localscript)

player = game.Players.LocalPlayer
person = Player.Character

while true do
if person.Health > 70 then
    script.Parent.Visible = true
end
if person.Health < 50 then
    script.Parent.Visible = false
wait()
end
end

I dont really know what you meant with the entire "Visible" part,But i assume that you meant a GUI with blood on it?