Run it
Copy the script and paste it into your executor.
local stroke = Instance.new("UIStroke")
stroke.Parent = MainFrame
stroke.Thickness = 5
stroke.ApplyStrokeMode = Enum.ApplyStrokeMode.Border
local hue = 0
task.spawn(function()
while true do
hue += 0.01
if hue > 1 then
hue = 0
end
stroke.Color = Color3.fromHSV(hue,1,1)
task.wait()
end
end)RainbowBorder script free

Universal