Why is This Tween/Coroutine Loop to Repeatedly Change Colours Not Working?

I have quite a large sum of lightbulbs (spheres grouped together) that I would like to repeatedly Tween to a different colour and back simultaneously. I discovered that Tweening alone would not work, for the lightbulbs merely changed colour one at a time, as opposed to all at once. Therefore, I tried coroutining. With the script I’m currently using, however, none of the lightbulbs change whatsoever, and the output does not give any clue as to where I’ve gone wrong. If anyone could point out the error(s) in my script, it would be very much appreciated.

local Model = workspace.Colourful.Lightbulbs
local TweenService = game:GetService("TweenService")
local tweenInfo = TweenInfo.new(1,Enum.EasingStyle.Linear,Enum.EasingDirection.InOut,0,false,0)
local Goal1 = {Color = Color3.fromRGB(100, 100, 100)}
local Goal2 = {Color = Color3.fromRGB(255, 195, 155)}

while true do
    wait()
    coroutine.resume(coroutine.create(function()
        for i, part in pairs(Model:GetChildren()) do
            if part:IsA("BasePart") then
                local tween1 = TweenService:Create(part, tweenInfo, Goal1)
                tween1:Play()
                tween1.Completed:Wait(1)
                local tween2 = TweenService:Create(part, tweenInfo, Goal2)
                tween2:Play()
                tween2.Completed:Wait(1)
            end
        end
    end))
    coroutine.yield()
end